The earthquake stress drops of the Jinggu M_S6.6 and Ludian M_S6.5 earthquake sequences in Yunnan are calculated on the basis of waveform data and seismic phase data after eliminating the effects of regional seismic wave attenuations and station site responses. The results show that the stress drop increases with magnitudes within the scope of this study. After eliminating the influence of the magnitude,the average value of stress drop in the Jinggu earthquake sequence is higher than that of the Ludian earthquake sequence at the same magnitude range. This may be related to the stress state in different regions. In terms of the changes of time and space of stress drop,before the M_S5.8 strong aftershock,the stress drop shows a process of “slow down-turning up-maintain high value” after the mainshock. Meanwhile,almost all the high stress drop earthquakes are distributed around the M_S5.8 strong aftershock. It shows that stress environment in the region is increasing after the mainshock. And after the M_S5.9 strong aftershock,stress drop rapidly declines to a relatively stable state. After the two earthquakes,the regional tectonic stress releases more fully,and its stress environment begins to reduce rapidly:For the Ludian earthquake sequence without subsequent strong aftershocks,the average value of stress drop is lower than the Jinggu earthquake sequence at the same magnitude range. At the same time,the stress drop of aftershock sequences almost does not change too much in time after the mainchock. Combining with the releasing characteristics of the main energy,the stress in the region is excessively released,and the subsequent stress in the region gradually returns to normal. This may be the reason why the activity of the Ludian aftershock is significantly weaker and there is no subsequent strong aftershock.