Abstract: In this paper, the focal mechanisms of small and moderate earthquakes which occurred in the west of Zhangbo seismic zone from October 2008 to October 2018 were inverted by using the Hash method which is popular in the modern international based on the first motion sign and amplitude ratio. Based on the obtaining focal mechanism solution, the variation characteristics of stress field before and after the Zhuolu M_S4.3 earthquake are further studied. The results show that the focal mechanism solutions in this region are mainly normal and strike-slip type, followed by reverse strike type, and the strike-slip type slightly increases after Zhuolu M_S4.3 earthquake compared with before the earthquake, indicating that the shear effect in this region is enhanced. The compressive stress axes is predominated NEE-SWW and the principal tensioning stress axes bearing is SSE-NNW. The zhuolu M_S4.3 earthquake occurred near the low-value edge of the consistent parameters of the focal mechanism.