Abstract: The spatial variation of ground motion is affected by source rupture process, transmission route and soil condition. At present, the research on coherence of ground motion mostly based on array measured data, which doesn’t have universality. In this paper, using dislocation model of seismic source, theoretical seismogram of random earthquake motion field in homogeneous and single medium was simulated by numerical method. Spatial coherence of surface earthquake motion field is investigated, according to a lot of calculation data. The results show that the laws of spatial coherence of ground motion reflected in numerical simulation results basically tallies with those reflected in measured data, which indicates that the analysis method and model adopted in the paper is reasonable. Besides, anisotropy exists in spatial coherence of ground motion with propagation direction of seismic wave, and fault strike is an important influence factor of spatial coherence of ground motion. The method in this paper is just a attempt for coherence of ground motion.