The article is the evaluation in the practice of risk assessment for city-states. The Pressure-State-Response (PSR) model was applied to the establishment of an environmental risk assessment indicator system. Environmental risk index (ERI) and each subsystem index were calculated through an analytic hierarchy process. It takes the municipal solid waste (MSW) in Macao as a case study to execute. The risk grading and the potential risk for the MSW in Macao were determined. The results showed that the ERI of the Macao's MSW remained at a medium level (Level III, 0.4-0.6) from 2000 to 2015, respectively, and increased gradually. Meanwhile, the future trend of the environmental risk of the MSW was predicted for Macao and the causes were analyzed. The environmental risk of the MSW in 2019 will achieve a high level (Level IV, 0.6-0.8), and the environment risk in 2041 will achieve an extremely high level (>0.8). For the first time, the research applied to the PSR model into the environmental risk assessment of MSW, this method is reasonable and feasible. Further research can provide a scientific basis for risk prevention management in city-states and can be of reference for other urbanized areas.