Earthquake early warning(EEW)is one of the effective means to reduce earthquake disaster. Magnitude measurement is the most difficult and important parameter in the early warning system. Considering the regional characteristics of magnitude estimation method for earthquake early warning,we used 120 seismic waveform data of M_L ≥ 2.0 and above of Inner Mongolia Seismological Network from 2016 to 2018,and calculated the characteristic period parameters by using the vertical displacement time history in P-wave 3S time window and the vertical displacement time history in P-wave full band,respectively. The formulas for calculating earthquake warning magnitude are obtained,and the results are compared and analyzed in this paper. We found that the results obtained by P-wave full-band relation are more convergent than those calculated by P-wave 3S fixed time window,and the correlation coefficient fitted by the relation is more close to 1,which can make a better estimation of the magnitude of early warning earthquakes. Finally,combined with the data processing results,the relationship between the speed and accuracy of earthquake early warning is discussed.