Abstract: Influenced by the complexity of power flow factors, the accuracy of identifying key weak lines in power grid is low. Therefore, the identification technology of key weak lines in power grid based on absolute power flow factors and the distance between superior and inferior solutions is proposed. On the basis of fully considering the influence of the active power transmitted by the generator to the load point on the power flow factor, the absolute power flow factor state of the power grid is analyzed. The original matrix of influencing factors of power grid absolute power flow factor is established, and the difference of influence degree of different factors on power grid absolute power flow factor is expressed by entropy weight parameters. The TOPSIS method is used to analyze the proximity between the state of the line to be evaluated and the optimal state sequence, to determine the weak state of the key lines of the power grid, and to identify the key weak lines of the power grid. In the test results, this method has low load reduction, high power flow transfer entropy and effective efficiency percentage, and can effectively identify the key weak lines of the power grid.