In order to research the mechanism of sympathetic inrush occurring in electric locomotive transformer, the mathematical model including traction power supply system, closing locomotive and operating locomotive is established, flux linkage analytical solutions of locomotives transformers flux are obtained by using Laplace transform. The flux variety processes of closing transformer and operating transformer are analyzed though building simulation model. By studying variation of sympathetic inrush under different conditions, the influencing factors of sympathetic inrush are obtained, and the influence of the inrush current and sympathetic on traction network voltage is analyzed. The results show that the inrush current of closing electric locomotive could cause sympathetic inrush of the operating electric locomotive and make the voltage of traction network drop and seriously distort, which provide a reference for abnormal tripping of traction power supply system. This work is supported by National Natural Science Foundation of China (No. U1134205).