Abstract: Medium voltage devices are high-power devices on the train, which are dispersed in various systems of the train and powered by the train auxiliary power supply system. Due to the inductance effect, the peak current during the start-up of medium voltage devices may have adverse effects on the safety and stability of the train auxiliary power supply system. To ensure the stable and reliable operation of the train auxiliary power supply system, it is necessary to effectively control the peak current generated during the start-up of medium voltage devices. Aiming at avoiding the adverse effects of peak current superposition of medium voltage loads on the train auxiliary power supply system and ensuring sufficient auxiliary power supply capacity in case of faults, this paper study the sequential start-up control method for medium voltage devices during the power on self-test stage of a train, the start-up control method for air conditioning compressors during train operation, and the load reduction start-up control method for medium voltage devices under fault conditions in the auxiliary power supply system based on the control logic of the Train Control and Management System (TCMS). The effectiveness of the proposed train medium voltage devices start-up control method under the constraints of auxiliary power supply reserve rate and peak starting current was preliminarily verified through laboratory simulation testing and real train testing on an operating line.