We selected Lushan Earthquake occurred in 2013 and Jiuzhaigou Earthquake in 2017 as case study to analyze the causes for the difference in measured magnitudes from different stations by remeasuring M_S(BB) magnitude in vertical component. The average M_S(BB)magnitude is 7.1 of 572 broadband seismic waveforms in Lushan earthquake, and the average is 6.9 of 603 waveforms in Jiuzhaigou earthquake meanwhile. The stations with the measured magnitude greater than M_S(BB)7.3 in the Lushan earthquake showed a NW-SE direction distribution, consistent with the fault tendency;Less than M_S(BB)7.0 showed a NE-SW distribution, consistent with the fault trend. The stations with the measured magnitude greater than M_S(BB)7.0 in the Jiuzhaigou earthquake showed a NE direction distribution. M_S(BB)6.8 or smaller ones showed a NW-SE distribution, consistent with the fault trend. The directivity distribution of stations that measured magnitude greater than the average shows no relationship with Doppler effect and the radiation pattern of the P wave. In comparing Lushan earthquake and Jiuzhaigou earthquake, after we removed the site response and the influence of instrument, the difference in the measured magnitude of the stations still exists. The difference in measured magnitude of stations influenced by other than Doppler effect, radiation pattern, instrument and site response. Considering comprehensively the influencing factors of the earthquake magnitude, the magnitudes difference between Lushan earthquake and Jiuzhaigou earthquake may be related to the propagation path of the seismic waves.