The traditional risk assessment of a power substation calculates the reliability of main electrical wiring based on the annual average failure rate of power equipment, which cannot reflect the time-varying fault risk of equipment and its influence on the power supply at load points. In this paper, the operating risk of the power equipment is considered as being influenced by two factors, namely the state of the equipment and external operating weather environment, and the operating risk of the equipment is quantified by a Proportional Hazards Model (PHM). Considering that the equipment state score based on a fault tree is decentralized and the influence degree of different components’ faults on the equipment outage is different, a fuzzy comprehensive evaluation method of the equipment state based on an Analytic Hierarchy Process (AHP) is established. On this basis, by taking the connectivity between the power incoming lines and the load points as the risk quantification index, a substation risk assessment model considering power supply connectivity is established. The effectiveness of the proposed method is verified by taking the IEEE-RTS79 system substation as the test object. The results show that the failure rate of the main equipment in different scenarios has significant impact on the substation risk assessment result. This demonstrates the necessity of short-term risk assessment and the feasibility of the proposed method. This work is supported by the National Natural Science Foundation of China-State Grid Joint Fund for Smart Grid (No. U1866603) and the Science and Technology Project of Guangzhou Power Supply Bureau (No. GZHKJXM080032KK 52170010).