Abstract: During the 14th five year plan, live working technology in distribution network is vigorously promoted in China to further improve the power supply reliability of users. Mobile transformer vehicle is an important tool to realize the uninterrupted operation project of distribution network. Its impact on the transient characteristics of power grid after grid connection will determine the reliability of power supply by bypass line. To solve this problem, the mathematical model of mobile transformer vehicle bypass operation is built by using Matlab / Simulink simulation platform, the influence of mobile transformer vehicle on the transient charac-teristics of user side current and voltage after grid connection is studied, and the suppression effect of different closing angle and closing resistance on transient characteristics is explored to reduce the influence of mobile transformer vehicle on grid connection transient characteristics, it has certain guiding significance for the actual bypass operation.