diff --git a/contracts/Git3.sol b/contracts/Git3.sol
index 64502d2..2a09d8c 100644
--- a/contracts/Git3.sol
+++ b/contracts/Git3.sol
@@ -111,12 +111,10 @@ contract Git3 {
     srs = nameToRefInfo[name];
 
     if (srs.hash1 == bytes32(0) && srs.hash2 == bytes8(0)) {
-      // first store refHash
+      // store refHash for the first time
       require(refs.length <= uint256(uint192(int192(-1))),"refs exceed valid length");
 
-
       _setRefInfo(nameToRefInfo[name],refHash,uint192(refs.length));
-      console.log("refs_length:",refs.length);
       refs.push(name);
     }else{
       // only update refHash 
@@ -126,14 +124,19 @@ contract Git3 {
 
   // delRef(path: string): Promise<Status>
   function delRef(string memory name) public {
+    // only execute `sload` once to reduce gas consumption
     refInfo memory srs;
     srs = nameToRefInfo[name];
+    uint256 refsLen = refs.length;
 
     require(srs.hash1 != bytes32(0) || srs.hash2 != bytes8(0),"Reference of this name does not exist");
 
-    refs[srs.index] = refs[refs.length - 1];
-    nameToRefInfo[refs[refs.length - 1]].index = srs.index;
-    delete refs[refs.length - 1];
+    require(srs.index < refsLen,"System Error: Invalid index");
+    if (srs.index < refsLen-1){
+      refs[srs.index] = refs[refsLen - 1];
+      nameToRefInfo[refs[refsLen - 1]].index = srs.index;
+    }
+    refs.pop();
     delete nameToRefInfo[name];
   }
 }
\ No newline at end of file
diff --git a/test/git3-test.js b/test/git3-test.js
index f987723..6b4628f 100644
--- a/test/git3-test.js
+++ b/test/git3-test.js
@@ -88,12 +88,19 @@ describe("Git3 Test", function () {
     expect(refs[0]).to.eql([data0,key0]);
     expect(refs[1]).to.eql([data1,key1]);
     expect(refs[2]).to.eql([data2,key2]);
+    expect(refs.length).to.eql(3);
 
     // check delRef 
     await git3.delRef(key0);
     refs = await git3.listRefs();
     expect(refs[0]).to.eql([data2,key2]);
     expect(refs[1]).to.eql([data1,key1]);
+    expect(refs.length).to.eql(2);
+
+    await git3.delRef(key1);
+    refs = await git3.listRefs();
+    expect(refs[0]).to.eql([data2,key2]);
+    expect(refs.length).to.eql(1);
 
   })