The security and stability control system is an important defense line to ensure the reliable operation of the power grid. Serious physical consequences can be caused by cyber attacks against the security and stability control system. In order to quantitatively evaluate the impact of cyber attacks on security and stability control system and solve the problem that the existing risk assessment methods do not fully consider the susceptibility of cyber attacks,a risk assessment method of security and stability control system considering the impact of cyber attacks is proposed. Firstly,the hierarchical structure of the security and stability control system is analyzed. Then,the risk points of cyber attacks on the stability control device body and device's inter-station communication from the three perspectives of attack object,attack methods,and attack consequences are analyzed. Secondly,the susceptibility of cyber attacks is quantified based on the fuzzy analytic hierarchy process,and a successful probability model of cyber attacks for security and stability control system is established combined with the defense unit model of cyber attacks built by Petri nets. Finally,the risk assessment is carried out on the standard and actual systems combined with the physical consequences and the probability of successful attacks. The risk values under two conditions of normal operation and cyber attack are calculated to verify the validity of the proposed model.