The invention discloses a power supply risk assessment method and system for a power system. The method comprises the following steps that an assessment component is determined according to operation requirements for the power system; power supply paths of the component are searched, and stored; the power supply range of the component is searched, and all devices within the power supply range of the component are determined and stored; and according to all the power supply paths of the component as well as all the devices within the power supply range, the risk of the component is graded, and a risk grade of the component is obtained. The accuracy of risk grading can be effectively improved. Risk assessment is based on technical support of the power grid scheduling system, operation data of the power system is obtained in real time, and the instantaneity and accuracy of power supply risk assessment are further improved.