Abstract: The northern section of Xiaojiang fault zone is the largest fracture structure in Baihetan hydropower station reservoir. Its characteristics and activities have a clear impact on migration and relocation near the reservoir. After studies of large scale investigation, fault zone quartz morphology scan and radon survey, the distribution characteristics of Xiaojiang fault zone is defined—-from north of Ningnan county, along the left bank of Jinsha River, passing Yongle, Luji, Liugu and extending to the south of Menggu. Quartz micro morphology statistical analysis and stress micro shape show that the fault activity is strong in the late Pleistocene. The facts that there are a quartz grain surface with representatives of the two sliding mode (creep and stick slip) stress micro shape combined, the stress micro shape of corrosion degree, stacking and cutting relationship, show that the fault slipped in the late Pleistocene of at least three sub-periods, at the early stage of the creep, advanced for stick slip. The potential seismic hazard evaluation suggests that possible earthquake magnitude of northern section of Xiaojiang fault zone is M_S6.8~M_S7.1. Therefore, there may be another strong shock in this area in the future.