In order to explore the influence of reservoir operation on the safety of urban water supply, the evaluation index system of water supply safety was constructed according to the three criteria of water supply source safety, water supply process safety and water users’ safety. Then the water supply safety status of Chushandian Reservoir’s water supply area was quantitatively analyzed based on the evaluation method of single index quantification-multiple index synthesis-poly criteria integration (SMI-P). The results show that the overall level of water supply safety of this area is relatively low which is at a level close to safe and quasi safe, but it is on the rise. The water supply safety degree of each evaluation index is greatly differentiated. With the improvement of urbanization level and the establishment of infrastructures, the water supply safety degree of the reservoir water supply area will be effectively improved. The proposed discriminant criterion, evaluation indices and case analysis can provide a reference for the evaluation of water supply safety.