According to the multi-station method and using digital seismic records in the Zipingpu reservoir，we studied the seismic velocity ratio． The result shows that the wave velocity ratios in the southwest area of Zipingpu reservoir are most between 1. 6 and 1. 8，and its average seismic wave velocity ratio is 1. 74． The wave-velocity ratio formed a pattern of normality，fall and earthquake occurrence． The probability of earthquake in the southwest area of reservoir affected by reservoir impounding was most pronounced，and there were more earthquakes in the water peak． Larger earthquakes in the southwest area of Zipingpu reservoir are corresponding to the unloading process in the reservoir and the falling of the wave velocity ratios． The average wave velocity ratio in the southwest area of Zipingpu reservoir was higher than the northeast area． It can therefore be inferred that the phenomenon is related to the fault distribution and the underground media of the region of the southwest area of Zipingpu reservoir．