The invention relates to a high robustness electric transmission line parameter estimating method based on a multi-time period PMU, which belongs to the power system scheduling automation field. In this method, a parameter estimating model constituted of an objective function and constraint conditions is established; the objective function is the smallest among residual error weighted sum squares in N time periods; based on the KKT complementary slack condition corresponding to the parameter estimating model, the parameter estimating model is solved to acquire an optimum solution X; the time periods are arranged in descending order according to the maximum residual error of each of the time period; the time period of the optimum residual error is recorded as k; if the maximum residual error in the time period is smaller than a measuring residual error threshold, the parameter estimation is finished; and the acquired optimum solution is used as the estimation result of the parameter. According to the invention, the analytical form of the optimum solution of the model is solved based on the KKT condition, thus the calculating efficiency is ensured to be high; through the exclusion of the damaged datum and the iterative process of the parameter estimation, the damaged datum are eliminated effectively, thus improving the accuracy of the parameter estimation and ensuring the practicality of the method.