The Maxianshan north margin fault with strike NW crossing through south of Lanzhou city is the most dangerous place for a future strong earthquake to the city. Using the hybrid source model and the method of stochastic synthesizing high-frequency ground motion, the strong ground motion field in Langzhou city and its vicinity from an earthquake with magnitude 6.5 on the western segment of the fault is forecasted in this paper, the spatial characteristics and pattern of the field is summarized.