In view of the problems existing in the risk assessment of power monitoring systems, such as incomplete system modeling, fuzzy evaluation opinions of experts, and lack of consideration of the overall risk of systems, a risk assessment method for power monitoring systems is proposed, which is based on the cloud model and improved evidence theory. Firstly, according to the structure and security requirements of a power monitoring system, the equipment, security objectives, and threats of the system are analyzed, and the overall risk assessment model of the system is built. Then, in combination with the FAHP and modified entropy weight method, the weight of each element is obtained by using the optimal combination weighting method. Finally, the comprehensive risk assessment of the power monitoring system is completed by the cloud model and improved evidence theory, and the risk level of the system is obtained. The simulations show that the method is feasible and effective, which provides a new idea for the security management of the power monitoring system.