diff --git a/contracts/AirDrop.sol b/contracts/AirDrop.sol
index 8678c088..80c49680 100644
--- a/contracts/AirDrop.sol
+++ b/contracts/AirDrop.sol
@@ -3,15 +3,17 @@ pragma solidity 0.6.4;
 import "./interface/IBEP20.sol";
 import "./interface/ITokenHub.sol";
 import "./interface/IAirDrop.sol";
+import "./interface/IParamSubscriber.sol";
 import "./lib/SafeMath.sol";
+import "./lib/BytesToTypes.sol";
 import "./System.sol";
 import "./MerkleProof.sol";
 
-contract AirDrop is IAirDrop, System {
+contract AirDrop is IAirDrop, IParamSubscriber, System {
     using SafeMath for uint256;
 
     string public constant sourceChainID = "Binance-Chain-Tigris"; // TODO: replace with the real chain id
-    address public constant approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
+    address public approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
     bytes32 public constant override merkleRoot = 0xad4aa415f872123b71db5d447df6bb417fa72c6a41737a82fdb5665e3edaa7c3; // TODO: replace with the real merkle root
 
     // This is a packed array of booleans.
@@ -59,7 +61,7 @@ contract AirDrop is IAirDrop, System {
         emit Claimed(tokenSymbol, msg.sender, amount);
     }
 
-    function _verifySignature(address account, bytes memory ownerSignature, bytes memory approvalSignature, bytes32 extra) private pure {
+    function _verifySignature(address account, bytes memory ownerSignature, bytes memory approvalSignature, bytes32 extra) private view {
         // Ensure the account is not the zero address
         require(account != address(0), "InvalidSignature");
 
@@ -163,4 +165,16 @@ contract AirDrop is IAirDrop, System {
         }
         return string(converted);
     }
+
+    /*********************** Param update ********************************/
+    function updateParam(string calldata key, bytes calldata value) external override onlyInit onlyGov{
+      if (Memory.compareStrings(key,"approvalAddress")) {
+        require(value.length == 20, "length of approvalAddress mismatch");
+        address newApprovalAddress = BytesToTypes.bytesToAddress(20, value);
+        approvalAddress = newApprovalAddress;
+      } else {
+        require(false, "unknown param");
+      }
+      emit paramChange(key,value);
+    }
 }
\ No newline at end of file
diff --git a/contracts/AirDrop.template b/contracts/AirDrop.template
index 68c4d7cb..823cb83d 100644
--- a/contracts/AirDrop.template
+++ b/contracts/AirDrop.template
@@ -3,7 +3,9 @@ pragma solidity 0.6.4;
 import "./interface/IBEP20.sol";
 import "./interface/ITokenHub.sol";
 import "./interface/IAirDrop.sol";
+import "./interface/IParamSubscriber.sol";
 import "./lib/SafeMath.sol";
+import "./lib/BytesToTypes.sol";
 import "./System.sol";
 import "./MerkleProof.sol";
 
@@ -12,19 +14,19 @@ contract AirDrop is IAirDrop, System {
 
     {% if network == 'local' %}
       string public constant sourceChainID = "Binance-Chain-Ganges"; // TODO: replace with the real chain id
-      address public constant approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
+      address public approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
       bytes32 public constant override merkleRoot = 0xad4aa415f872123b71db5d447df6bb417fa72c6a41737a82fdb5665e3edaa7c3; // TODO: replace with the real merkle root
     {% elif network == 'QA' %}
       string public constant sourceChainID = "Binance-Chain-Ganges"; // TODO: replace with the real chain id
-      address public constant approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
+      address public approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
       bytes32 public constant override merkleRoot = 0xad4aa415f872123b71db5d447df6bb417fa72c6a41737a82fdb5665e3edaa7c3; // TODO: replace with the real merkle root
     {% elif network == 'testnet' %}
       string public constant sourceChainID = "Binance-Chain-Ganges"; // TODO: replace with the real chain id
-      address public constant approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
+      address public approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
       bytes32 public constant override merkleRoot = 0xad4aa415f872123b71db5d447df6bb417fa72c6a41737a82fdb5665e3edaa7c3; // TODO: replace with the real merkle root
     {% else %}
       string public constant sourceChainID = "Binance-Chain-Tigris"; // TODO: replace with the real chain id
-      address public constant approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
+      address public approvalAddress = 0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa; // TODO: replace with the real address
       bytes32 public constant override merkleRoot = 0xad4aa415f872123b71db5d447df6bb417fa72c6a41737a82fdb5665e3edaa7c3; // TODO: replace with the real merkle root
     {% endif %}
     // This is a packed array of booleans.
@@ -72,7 +74,7 @@ contract AirDrop is IAirDrop, System {
         emit Claimed(tokenSymbol, msg.sender, amount);
     }
 
-    function _verifySignature(address account, bytes memory ownerSignature, bytes memory approvalSignature, bytes32 extra) private pure {
+    function _verifySignature(address account, bytes memory ownerSignature, bytes memory approvalSignature, bytes32 extra) private view {
         // Ensure the account is not the zero address
         require(account != address(0), "InvalidSignature");
 
@@ -176,4 +178,16 @@ contract AirDrop is IAirDrop, System {
         }
         return string(converted);
     }
+
+    /*********************** Param update ********************************/
+    function updateParam(string calldata key, bytes calldata value) external override onlyInit onlyGov{
+      if (Memory.compareStrings(key,"approvalAddress")) {
+        require(value.length == 20, "length of approvalAddress mismatch");
+        address newApprovalAddress = BytesToTypes.bytesToAddress(20, value);
+        approvalAddress = newApprovalAddress;
+      } else {
+        require(false, "unknown param");
+      }
+      emit paramChange(key,value);
+    }
 }
\ No newline at end of file
diff --git a/contracts/interface/IAirDrop.sol b/contracts/interface/IAirDrop.sol
index 5c18ec76..9f2029d9 100644
--- a/contracts/interface/IAirDrop.sol
+++ b/contracts/interface/IAirDrop.sol
@@ -12,4 +12,6 @@ interface IAirDrop {
         bytes32[] calldata merkleProof) external;
     // This event is triggered whenever a call to #claim succeeds.
     event Claimed(bytes32 tokenSymbol, address account, uint256 amount);
+    // This event is triggered whenever a call to #paramChange succeeds.
+    event paramChange(string key, bytes value);
 }