Based on the model of stochastic medium and the model of composite focus,the spatial distribution and time sequence of microquakes and the magnitude-frequency correlation were discussed by using finite element numerical simulation in this paper.The results show that the disorder of the spatial distribution of microquakes in initial stage was translated to the order in main-shock stage.The precursors are characterized by the propagation from periphery to center.In addition,the linear relation between magnitude and frequency only exists in the middle magnitude range and very large deviation exists in the high and low magnitude ranges.