The invention provides an overhead transmission line optimal economic life range assessment method. The error of a failure rate prediction result of electric transmission and transformation equipment and the subjectivity of rough calculation of partial parameters of the full-life cycle cost cause an economic life result obtained by the adoption of setting calculation to have certain deviation. The overhead transmission line optimal economic life range assessment method comprises the steps that the fuzzy comprehensive evaluation method and the analytic hierarchy process are used for calculating membership degrees of all indexes and weights of all the indexes respectively; then, training output and error calculation are conducted on three failure rates of a transmission line through a least square support vector machine together with the relevant data of the service age, the external operation environment and the quality condition of the transmission line respectively, and a failure rate prediction model of the transmission line is obtained; finally, the interval analysis method is introduced into the life cycle cost theory and the optimal economic life range of the transmission line is obtained at last. According to the overhead transmission line optimal economic life range assessment method, the characteristics that the wild operation environment of the transmission line is poor and the regional span of the transmission line is wide are fully considered, and meanwhile, the problem that for different transmission lines, a uniform life ending standard is hard to provide is solved.