Based on digital seismic waveform data from the Inner Mongolia Digital Seismic Network,source spectrum parameters of 182 small and moderate earthquakes from January 2009 to September 2016 are derived and the seismic moment M₀ and moment magnitude M_W of the earthquakes are calculated. The M_L-M_W relational expression between stress drop and magnitude are obtained using linear regression method. Visible incorporating the moment magnitude can enrich the earthquake observation report content,and provide better service for earthquake emergency and earthquake scientific research.