Abstract: Based on the method of initial motion and amplitude-ratio developed by Snoke, the focal mechanisms of 41 moderate and small earthquakes occurred in Capital Area are calculated with 1028 seismic waveform data recorded by 59 three-components digital observatories from 2002 to Jan.2004, And the reliability of the focal mechanism solutions is tested with random model method.The results show that the focal mechanisms in the region have regionality, such as reversal faulting dominates in Tangshan area, and normal faulting dominates in Beijing-Tianjin area.