Because of the randomness and uncertainties of earthquake and its structures, it is a natural choice to analyze and evaluate the risk of earthquake in the way of seismic risk analysis. Effective prediction of earthquakes can minimize property losses and protect citizens’ safety. In this article, Bayes rule was used to make a simple prediction of the risk of a strong earthquake in a certain area. Then we conducted probabilistic seismic risk analysis (PSHA) to tackle the problem of a specific earthquake about where the earthquake will occur, how big the earthquake will be and when will the earthquake occur. Furthermore, we dived into spatial uncertainty, temporal uncertainty, and size uncertainty, respectively. Since earthquake intensity is significant for seismic vulnerability analysis, PGA (peak ground acceleration) was used as the index of earthquake intensity in this article. To be more specific, Wenchuan city in Sichuan province in China was chosen as the subject. Finally, seismic risk analysis was performed and the failure probability of the system was gained.