We evaluate the operation risk of overhead transmission lines under the combined action of multiple natural disasters. The analysis is based on modern security risk quantification theory, fully considering the possibility of various natural disaster risks, the degree of impact on overhead transmission lines, the severity of the hazards, the risk probability, line failure transmission capacity loss value, and risk social impact coefficient. These are used to comprehensively quantify the disaster operation risk of overhead lines. It establishes a risk assessment system for the operation of overhead transmission lines under various natural disasters, and uses the improved analytic hierarchy process to calculate the risk weights of different natural disasters, to ensure the rationality of assessment results. This method is used to complete an operational risk assessment of a regional power grid overhead transmission line under multiple natural disasters. This verifies the feasibility of the method. The evaluation method proposed is versatile, and the results can provide a basis for taking targeted disaster prevention measures and improve the risk prevention capabilities of lines. This work is supported by the National Natural Science Foundation of China (No. 51507119) and the Science and Technology Project of State Grid Henan Electric Power Company (No. 5217H020000K).