Abstract: Water conservancy and hydropower projects have a long construction period and a large amount of wastewater discharge. If it is directly discharged without treatment,it will have adverse effects on the water environment. Taking Xulong hydropower station of Jinshajiang River as an example,this paper studies the impact of sand and gravel processing system and domestic sewage accident discharge on the water environment of Jinsha River. The results show that:in the case of accident discharge,the horizontal impact of domestic sewage is concentrated in the range of 4 m away from the bank,and the longitudinal impact is concentrated in the range of 200 m downstream of the sewage outlet.The maximum increment of COD concentration at the outlet is 0.5 mg/L compared with the background concentration;the length of SS pollution zone can reach 16.5 km in the case of accident discharge of waste water from sand and gravel processing system S concentration is about13.4 times of river background value. The results can provide a scientific reference for the study of water environmental impact during the construction period of hydropower projects,and provide support for the selection of risk prevention measures of waste water accident discharge during the construction period of Xulong hydropower station.