diff --git a/lib/helper/utils.ex b/lib/helper/utils.ex
index a522a6788..5afd540a8 100644
--- a/lib/helper/utils.ex
+++ b/lib/helper/utils.ex
@@ -246,4 +246,40 @@ defmodule Helper.Utils do
   end
 
   def str_occurence(_, _), do: "must be strings"
+
+  @spec large_than(String.t() | Integer.t(), Integer.t()) :: true | false
+  def large_than(value, target) when is_binary(value) and is_integer(target) do
+    String.length(value) >= target
+  end
+
+  def large_than(value, target) when is_integer(value) and is_integer(target) do
+    value >= target
+  end
+
+  @spec large_than(String.t() | Integer.t(), Integer.t(), :no_equal) :: true | false
+  def large_than(value, target, :no_equal) when is_binary(value) and is_integer(target) do
+    String.length(value) > target
+  end
+
+  def large_than(value, target, :no_equal) when is_integer(value) and is_integer(target) do
+    value > target
+  end
+
+  @spec less_than(String.t() | Integer.t(), Integer.t()) :: true | false
+  def less_than(value, target) when is_binary(value) and is_integer(target) do
+    String.length(value) <= target
+  end
+
+  def less_than(value, target) when is_integer(value) and is_integer(target) do
+    value <= target
+  end
+
+  @spec less_than(String.t() | Integer.t(), Integer.t(), :no_equal) :: true | false
+  def less_than(value, target, :no_equal) when is_binary(value) and is_integer(target) do
+    String.length(value) < target
+  end
+
+  def less_than(value, target, :no_equal) when is_integer(value) and is_integer(target) do
+    value < target
+  end
 end
diff --git a/lib/helper/validator/guards.ex b/lib/helper/validator/guards.ex
new file mode 100644
index 000000000..6aa4c8b7a
--- /dev/null
+++ b/lib/helper/validator/guards.ex
@@ -0,0 +1,7 @@
+defmodule Helper.Validator.Guards do
+  @moduledoc """
+  general guards
+  """
+  defguard g_pos_int(value) when is_integer(value) and value >= 0
+  defguard g_not_nil(value) when not is_nil(value)
+end
diff --git a/lib/helper/validator/schema.ex b/lib/helper/validator/schema.ex
index 2f847f317..3aabd54a6 100644
--- a/lib/helper/validator/schema.ex
+++ b/lib/helper/validator/schema.ex
@@ -23,6 +23,13 @@ defmodule Helper.Validator.Schema do
   data = %{checked: true, label: "done"}
   Schema.cast(schema, data)
   """
+
+  alias Helper.Utils
+  import Helper.Validator.Guards, only: [g_pos_int: 1, g_not_nil: 1]
+
+  @support_min [:string, :number]
+
+  @spec cast(map, map) :: {:ok, :pass} | {:error, map}
   def cast(schema, data) do
     errors_info = cast_errors(schema, data)
 
@@ -62,11 +69,8 @@ defmodule Helper.Validator.Schema do
         {:ok, value}
 
       false ->
-        {:error,
-         %{
-           field: field,
-           message: "should be: #{enum |> Enum.join(" | ")}"
-         }}
+        msg = %{field: field, message: "should be: #{enum |> Enum.join(" | ")}"}
+        {:error, msg}
     end
   end
 
@@ -78,22 +82,11 @@ defmodule Helper.Validator.Schema do
   end
 
   # custom validate logic
-  defp match(field, value, :string, [{:min, min} | options])
-       when is_binary(value) and is_integer(min) do
-    case String.length(value) >= min do
-      true ->
-        match(field, value, :string, options)
-
-      false ->
-        error(field, value, :min, min)
-    end
-  end
-
-  defp match(field, value, :number, [{:min, min} | options])
-       when is_integer(value) and is_integer(min) do
-    case value >= min do
+  defp match(field, value, type, [{:min, min} | options])
+       when type in @support_min and g_not_nil(value) and g_pos_int(min) do
+    case Utils.large_than(value, min) do
       true ->
-        match(field, value, :number, options)
+        match(field, value, type, options)
 
       false ->
         error(field, value, :min, min)
@@ -109,13 +102,14 @@ defmodule Helper.Validator.Schema do
   defp match(field, value, :boolean, []) when is_boolean(value), do: done(field, value)
   # main type end
 
-  # judge option
+  # error for option
   defp match(field, value, type, [option]) when is_tuple(option) do
     # 如果这里不判断的话会和下面的 match 冲突，是否有更好的写法？
     case option_valid?(option) do
       true ->
         error(field, value, type)
 
+      # unknow option or option not valid
       false ->
         {k, v} = option
         error(field, value, option: "#{to_string(k)}: #{to_string(v)}")
diff --git a/test/helper/utils_test.exs b/test/helper/utils_test.exs
index ec5e43b94..228690048 100644
--- a/test/helper/utils_test.exs
+++ b/test/helper/utils_test.exs
@@ -128,4 +128,38 @@ defmodule GroupherServer.Test.Helper.UtilsTest do
       assert 0 == Utils.str_occurence("hello world", "foo")
     end
   end
+
+  describe "[basic compare]" do
+    test "large_than work for both number and string" do
+      assert true == Utils.large_than(10, 9)
+      assert false == Utils.large_than(8, 9)
+
+      assert true == Utils.large_than("lang", 3)
+      assert false == Utils.large_than("ok", 3)
+    end
+
+    test "large_than equal case" do
+      assert true == Utils.large_than(9, 9)
+      assert false == Utils.large_than(9, 9, :no_equal)
+
+      assert true == Utils.large_than("lang", 4)
+      assert false == Utils.large_than("lang", 4, :no_equal)
+    end
+
+    test "less_than work for both number and string" do
+      assert false == Utils.less_than(10, 9)
+      assert true == Utils.less_than(8, 9)
+
+      assert false == Utils.less_than("lang", 3)
+      assert true == Utils.less_than("ok", 3)
+    end
+
+    test "less_than equal case" do
+      assert true == Utils.less_than(9, 9)
+      assert false == Utils.less_than(9, 9, :no_equal)
+
+      assert true == Utils.less_than("lang", 4)
+      assert false == Utils.less_than("lang", 4, :no_equal)
+    end
+  end
 end
diff --git a/test/helper/validator/schema_test.exs b/test/helper/validator/schema_test.exs
index fae9c0d71..690204f03 100644
--- a/test/helper/validator/schema_test.exs
+++ b/test/helper/validator/schema_test.exs
@@ -85,7 +85,6 @@ defmodule GroupherServer.Test.Helper.Validator.Schema do
       # hello world
     end
 
-    @tag :wip2
     test "number with wrong option" do
       schema = %{"text" => [:number, required: true, min: "5"]}
       data = %{"text" => 1}