diff --git a/package.json b/package.json
index 1f87311..ae3c419 100644
--- a/package.json
+++ b/package.json
@@ -16,6 +16,7 @@
   "license": "ISC",
   "dependencies": {
     "async": "^2.6.2",
+    "biguint-format": "^1.0.1",
     "bluebird": "^3.5.3",
     "bunyan": "^1.8.12",
     "cheerio": "^1.0.0-rc.3",
diff --git a/src/utils/string.util.js b/src/utils/string.util.js
index 13f8d3f..edd4219 100644
--- a/src/utils/string.util.js
+++ b/src/utils/string.util.js
@@ -1,3 +1,5 @@
+import crypto from "crypto";
+import format from 'biguint-format';
 
 export default {
   /**
@@ -35,8 +37,12 @@ export default {
     }
     return result;
   },
+  // randomNum(minNum, maxNum) {
+  //   return parseInt(Math.random()*(maxNum-minNum+1)+minNum, 10);
+  // },
   randomNum(minNum, maxNum) {
-    return parseInt(Math.random()*(maxNum-minNum+1)+minNum, 10);
+    let x = format(crypto.randomBytes(4), 'dec');
+    return parseInt(x / Math.pow(2, 4 * 8) * (maxNum + 1 - minNum) + minNum);
   },
   getContentByReg(str, reg) {
     const contents = str.match(reg);