The impact of time-varying lightning on electrical equipment fault probability is analyzed.Based on the information to be acquired for preventing lightning disaster，a spatial-temporal variation forecast algorithm for power grid fault probability is presented.First，according to the lightning information of the current time interval，the lightning subareas are duly divided，which should be associated with the subareas in the preceding time interval.Then，according to the results，the trend of lightning fault probability in the next time interval is forecasted.The spatial-temporal distributed prediction probability is used to replace the traditional average annual lightning fault probability in the method which updates the envisioned fault table of the security stability analysis software online，enables the faults with greater probability to get detailed analysis in time and realizes the integration with power system security stability analysis function.The self-adaptive ability to deal with lightning disaster is added to actual projects of the blackout prevention system to improve the early-warning ability.