Hydraulic fracturing and piezomagnetic overcoring insitu stress measurements were carried out in two boreholes in the southwestern Longmenshan Fault Zone to understand the current insitu stress state and stress change after the Lushan Ms 7.0 earthquake on the April 20th, 2013. Measurement results show that the maximum horizontal principal stress and minimum horizontal principal stress at the Qiaoqi borehole is 19.60~25.83 MPa and 10.47~18.47 MPa within the depth of 128~188 m, with an orientation of N63°~85°W; the maximum horizontal principal stress and minimum horizontal principal stress at the Tianquan borehole is 8.21~9.31 MPa and 5.20~7.73 MPa within the depth range of 114~142m, with an orientation of N59°W. Relationships between horizontal stress and vertical stress of the two measuring points are σH>σh>σv. The average ratios of maximum and minimum horizontal stress to vertical stress at the Qiaoqi borehole are 5.27 and 3.01 respectively. The average ratios of maximum and minimum horizontal stress to vertical stress at the Tianquan borehole are 2.60 and 1.76 respectively. The results that horizontal stress is higher than vertical stress will lead to a reverse fault activity. Comparison of insite stress states in this area before and after the Lushan earthquake suggests that after the earthquake the accumulation of stress of the unbroken active faults on both sides of the epicenter has been increasing. What's more, the stress magnitude at the Qiaoqi borehole improves significantly after the earthquake, which is in consistent with the monitoring results at the Qiaoqi. On the basis of insitu stress data and Coulomb faulting criterion, the maximum horizontal principal stress at Qiaoqi was between the minimum and the maximum of fault slip before the earthquake, and exceeded the maximum after the earthquake. The maximum horizontal principal stress at Feixianguan was lower than the maximum of fault slip before earthquake.μm, the ratio between the maximum horizontal principal stress \[(σ1-σ3)/2\] and average stress \[(σ1+σ3)/2\], can be used to evaluate the present stress accumulation level and the seismic risk. The preearthquakeμmvalue at Qiaoqi was 0.16~0.72, with an average of 0.50, and the postearthquake μm value at Qiaoqi is 0.71~0.81, with an average value of 0.77. The preearthquake μmvalue at Feixianguan was 0.31~0.35, with an average of 0.32, and the postearthquake μm value at Tianquan was 0.53~0.57, with an average value of 0.55.μm values in two study areas show a big difference. This study concludes that the stress in the northern and southern segments of the Longshan fault zone has been accumulated, which can increase possibility of fault slipping, especially in the northern segment.