A fast online early warning method for power grid protection relay setting based on mode change effect range identification and fault calculation result ordering is proposed. This method uses the rate of change of current and branch coefficient value at protection relay installation point to determine the protection relays that should change their setting values to accommodate the tripping off of line or transformer. And in order to further improve the speed of the on-line analysis of the protection relay setting, the order optimization of the short circuit calculation result is carried out. Thus the online early warning of protection relay setting can be achieved. The practical application shows that this method can quickly and accurately warn the special operation mode and protection relay of the power grid with hidden danger. This work is supported by National Natural Science Foundation of China (No. 51777081) and Science and Technology Project of Guangdong Power Grid Co., Ltd. (No. GDKJQQ20161176).