Abstract: A risk assessment method for reactor decommissioning was established. The method comprises five procedures: source analysis, hazard analysis, frequency analysis, accident consequence analysis and risk analysis. Based on the method, the reactor decommissioning risk assessment system (RDRAS) was developed. 53 situations of the 11 activities that may arise in the HWRR decommissioning process were modeled and calculated with RDRAS to identify the radioactive risk that working staff may face in each situation, and the uncertainties of the results were analyzed.