The arrangement of current transmission line patrol plan has the problem of low inspection efifiency. In order to optimize the patrol plan and reduce the patrol cost of transmission lines , this paper proposes an optimization method of transmission line patrol plan based on dynamic risk assessment. Considering the internal and external risks of transmission line faults and the losses caused by faults, a dynamic risk level evaluation model is established , and the reasonable patrol period is determined by quantifying the risk value to evaluate the line risk level. The multi-objective optimization model of transmission line patrol plan is established based on the patrol period, and the multi-objective particle swarm optimization alorithm is used to solve the problem according to the priority of the objective. The validity of the proposed model is verified by the actual transmission line in a certain region.