Abstract: Referring to the risk ranking methodology of groundwater contamination both at home and abroad and based on the comprehensive analysis on the key points of the groundwater pollution risk in the contaminated sites, the analytic hierarchy process was applied to establish the risk ranking index system on groundwater pollution of contaminated sites from three aspects, i.e. the contaminated sites properties, the groundwater inherent vulnerability in the contaminated sites region and the characteristics of the groundwater protection target. The risk ranking index system consists of 17 indicators. Based on the survey on contaminated sites and the physical and chemical properties of 159 typical pollutants, the risk level for each indicator was ranked. The total risk index was calculated by multiplying the individual risk indicators, and the method of groundwater pollution of contaminated sites was established by applying the clustering analysis. The method can effectively avoid the subjectivity of index weight calculation, and ide.pngy the main factors that lead to the risk. The results showed that the risk of groundwater pollution of contaminated sites could be divided into 3 levels, i.e. the risk value less than 5 (Level 1), between 5 and 15 (Level 2) and greater than 15 (Level 3). By applying the risk assessment system in a hazardous waste landfill, it was shown that the landfill had a potential risk of Level 3, and the properties of the contaminated sites, especially the characteristic pollutant was the main factors that caused the groundwater environmental risk.