Abstract: Based on the broadband digital seismic records of Inner Mongolia seismic network, using CAP method and TDMT-INVC method, the focal mechanism solution of Helinger M4.0 earthquake on March 30, 2020 is calculated. In addition, the depth is further determined by using the method of sPn and Pn phase travel time difference. The results show that the focal mechanism solutions determined by the two methods are basically consistent, the focal mechanism is mainly strike slip with a slight thrust component. The focal depth measured by CAP method and sPn and Pn phase travel time difference method has good consistency, and the distribution range is 14.0 ~ 15.5 km, which indicates that the earthquake occurred in the upper crust, which is in line with the distribution characteristics of earthquake sources in this region.