Abstract: Fault is one of the important factors leading to geological disasters. In order to ensure the safety of engineering projects, it is necessary to determine the activity of fault to avoid geological disasters. There is a NW fault located within the proposed Budaigou Tailing Reservoir area. Taking the fault as an example, the fault in the proposed reservoir area is investigated through methods such as geological survey, geophysical exploration (high density resistivity and electrical sounding), drilling and trench excavation. The fault is 1.55 km long and 1.5~2.5 km wide normal fault, northwest extending. The occurrence is 70°∠72°, and control depth being 420 m. The fault is a small non-holocene active fault with no obvious activity since Quaternary. The stability of fault engineering is good, which has no influence on engineering construction. However, considering the existence of fault structure breccia, although it has been consolidated, it is easy to be weathered relative to the surrounding rock, forming a certain loose layer, which may cause groundwater infiltration channel.So it is recommended to pay attention to it in engineering construction.