In the process of technical renovation for the monitoring and control system, there are four typical faults: false alarm signals, abnormal data communication in dispatch communication system, slow data refreshing of the 101 communication protocol and AGC/AVC workstation crash. Through analysis, we found that these faults are caused by circuit electromagnetic interference, software bugs, ill-considered procedures, outdated firmware version and unreasonable allocation in calculation procedures, respectively. We can solve all the faults by strengthening circuit anti-interference ability and filtering signals in the program, removing program bugs , reasonably arranging the start-stop time and orders in processing sequence, optimizing process and strategies to reduce the amount of data sent and shorten the queues length, upgrading the firmware version, and optimizing the load distribution of calculation program to avoid halt of AGC/AVC workstation system. Results show that the measures are effective.