Abstract: In this paper, the calibrating function of local earthqukes at Inner Mongolia area is discussed based on the observation data of 28 stations in this area, and by the analysis of the magnitude deviation and the estimation of the average attenuation patterns of maximum seismic phase of near earthquakes. Each station correction is also estimated. Then, the magnitude system of local earthquakes at Inner Mongolia area is set up. The statistical results indicate th average error of magnitude M_L has been obviously decreased by this system.