At present, the inspection cycle of transmission lines is mostly fixed, which can not be adjusted in time according to the operation status and environmental conditions of the lines, which affects the reliability and economic operation of power supply. To solve this problem, an optimal inspection strategy of overhead transmission lines considering time-varying failure rate is proposed. The model of inspection strategy based on genetic algorithm is established with the maximum comprehensive objective benefit function including inspection cost, failure power loss cost and maintenance reliability cost as the index. In order to establish a more accurate benefit function, a non-time homogeneous Markov time-varying outage model is established, and the reliability index is obtained by combining with Monte Carlo reliability simulation model. Finally, a dynamic and periodic variable transmission line inspection plan is solved by genetic algorithm. Through the calculation of the two regions with different fault rate characteristics, it is shown that the algorithm can make the inspection strategy according to the actual fault rate of transmission lines, and get an economic, reasonable, regional, seasonal and dynamic variable inspection cycle plan. It avoids the problem of over inspection and insufficient inspection, and can achieve greater economic efficiency under the favorable condition, the transmission line can operate in a better state. This work is supported by Youth Fund of National Natural Science Foundation of China (No. 51007066).