In view of the deficiency of risk based maintenance assistant decision-making in engineering practice, a risk assessment technique for power equipment based on topology modeling and association sets decomposition is proposed. Based on the analysis of IEC61970 standard CIM data, the equivalent model of power grid topology is established, and the concept of Equipment Association Set is introduced as the basic unit of risk assessment for simplified analysis. Based on the outage model, the contingency screening strategy and the optimal load shedding model, the N-1 operational risk caused by the association set outage is evaluated. The application example of Shandong power grid has demonstrated the guidance significance of the proposed technique for maintenance decision. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015AA050204) and Science and Technology Project of State Grid Corporation of China (No. 520626150032).