Based on digital seismic waveform data in Yunnan seismic network, we inversed the source spectrum pa- rameters and calculated the seismic moment M0 and moment magnitude Mw of 675 moderate and small earth- quakes form Jan. , 2008 to Sep. , 2012. Finally, we obtained the relationship expression between body wave magnitude ML and moment magnitude Mw of local earthquake by linear regression analysis method.