Source parameters of 1070 earthquakes with M_L≥3.0 in Wenchuan aftershocks were calculated after taking away the effects due to earthquake anelastic attenuation and site response accurately, using partial seismic data selected from Wenchuan M8.0 aftershocks in 2008 recorded by the fixed seismograph network of Sichuan province. These results show that there is a linear relation between seismic moment and magnitude, and the stress drop and apparent stress increase with increasing magnitude. The temporal and spatial evolution process of stress drop derived from seismic data with M_L3.0 shows that the stress drop of Wenchuan aftershocks decays with time as a whole after the mainshock occurred. Divided along Huya-Beichuan-Anxian, the activity level and stress drop in the Longmenshan fault 〖JP2〗appear to be segmental. Aftershocks with M_L≥5.0 〖JP〗mainly occurred at the west of Beichuan in the Longmenshan fault and the values of stress drop in this area are lower before May 17. Meanwhile, the activity level between Beichaun and Qinchuan is weak comparatively and the stress drop in there maintains a high level. However, aftershocks with M_L≥5.0 changed to occur between Beichaun and Qinchuan after May 17 and the biggest aftershock of M6.4 in Qinchuan occurred here on May 25 and the change of stress drop with time of the aftershocks appears to become smooth since then.