Abstract: A small local failure block in surrounding slope of hydropower project can become a big potential hazard for hydraulic construction(structure) building and human security. So the assessment of surrounding slope has to pay more attention to the stability investigation and assessment of the local and small block. There are a total of 100 hazard sources existing in surrounding slope of Busigou hydropower project.61 of them are developed in the left bank and 39 in the right bank. Based on a large number of precise field investigation and analysis, a classification is proposed according to geological genesis, scale and failure mechanism respectively. According to geological genesis, hazard sources are divided into four types: (group of )isolated stone,(group of )dangerous rock(generally100m3),dangerous rock mass and high position covering layer. Considering the hazard stability and degree of project importance, hazard rating assessment system(HRAS) of surrounding slope which has enough easily valued indicators is established according to three first level indicators(the hazard source, path and inducing factors),nine secondary indicators(stability, potential energy, hazard sources' shape, path's geometric features, vegetation growth, earthquake and rainfall), and 35 basic indicators. According to the level of values, hazard rating is divided into three levelshigh, medium, and low level. Using this assessment system to evaluate the hazard rating of surrounding slope of Busigou hydropower project, the evaluation results show that in the total of 100 hazard sources,19 are of high hazard rating, 55 of medium and 26 of low hazard sources. The result is largely correspondence to reality. This assessment system has some engineering significance for hazard source prevention and controlling.