Abstract: According to the difference of typical current between normal circuit and fault circuit, based on S Transform and K-means clustering, it proposed the fault identification method of transmission line. By means of S transform, it obtained the fault characteristic of line typical current. By using the entropy weight method to calculate the comprehensive relative entropy and find out the difference of lines. Then, it used the K-means clustering method to identify the fault transmission lines. The simulation experiment results showed that the fault identification method had high accuracy and strong adaptability.