Abstract: In this paper, according to the P wave data recorded by seismographs at the basic stations in China,a comprehensive study is made on the focal process of the Menyuan M6.4 earthquake in Qinghai Province occurred on August 26,1986 and the focal dynamic parameters are obtained.The result shows that the seismic structure of the Menyuan earthquake strikes NE50°, showing an unilateral fracture striking NE, with fracture lenght being 20 km and average fracture velocity being 1.83km/s.