diff --git a/src/collator/CollatorSet.sol b/src/collator/CollatorSet.sol
index ac8d006..821d9d5 100644
--- a/src/collator/CollatorSet.sol
+++ b/src/collator/CollatorSet.sol
@@ -17,6 +17,13 @@ abstract contract CollatorSet is Initializable, CollatorStakingHubStorage {
         votesOf[HEAD] = type(uint256).max;
     }
 
+    /// @dev Fetch top k collators in ordered collator set.
+    /// @param `k` Count of top collators.
+    /// @return The `k` top collators.
+    /// *Note*  The result of top collators length is always be `k`.
+    ///         If the length of collator set `len` is less than `k`,
+    ///         the array result of first `len` is filled by nomal collators
+    ///         and the rest of `len - k` collators is filled by address(0)
     function getTopCollators(uint256 k) public view returns (address[] memory) {
         address[] memory topCollators = new address[](k);
         uint256 len = count;
diff --git a/src/collator/CollatorStakingHub.sol b/src/collator/CollatorStakingHub.sol
index 5e01141..7e9aeb9 100644
--- a/src/collator/CollatorStakingHub.sol
+++ b/src/collator/CollatorStakingHub.sol
@@ -141,6 +141,10 @@ contract CollatorStakingHub is Initializable, ReentrancyGuardUpgradeable, Collat
         _addCollator(collator, _assetsToVotes(commission, stakedOf(collator)), newPrev);
     }
 
+    /// @dev Distribute collator reward from Staking Pallet Account.
+    ///      The amount of the reward must be passed in via msg.value.
+    /// @notice Only Staking Pallet Account could call this function.
+    /// @param collator The collator address to distribute reward.
     function distributeReward(address collator) public payable onlySystem nonReentrant {
         address pool = poolOf[collator];
         require(pool != address(0), "!collator");
diff --git a/src/deposit/Deposit.sol b/src/deposit/Deposit.sol
index 46dcc30..fb932d2 100644
--- a/src/deposit/Deposit.sol
+++ b/src/deposit/Deposit.sol
@@ -105,6 +105,12 @@ contract Deposit is
         _disableInitializers();
     }
 
+    /// @dev Migrate user's deposit from Deposit Pallet to Deposit smart contract.
+    ///      The amount of the deposit value must be passed in via msg.value.
+    /// @notice Only Deposit Pallet Account could call this function.
+    /// @param account The user account address stored in Deposit Pallet.
+    /// @param months The user deposit months stored in Deposit Pallet.
+    /// @param startAt The user deposit start time stored in Deposit Pallet.
     function migrate(address account, uint64 months, uint64 startAt) external payable onlySystem nonReentrant {
         uint256 value = msg.value;
         require(value > 0 && value < type(uint128).max, "!value");