The high voltage substation of urban rail transit occupies a decisive position in city rail power supply system, in order to grasp its load characteristics, evaluate its power supply capability and reliability, and guide the design of the high voltage transformer capacity, this paper carries out statistics on load test data of the high voltage substation of existing operation line. The statistics show that the high voltage transformer's load factor of the main transformer in peak hours is mostly between 37%~53% and the load rate is between 11%~48%. At the same time, supposing the main transformer substation only uses one incoming line of power supply system, the load factor of the high voltage substation is between 41%~48%, the load rate of the high voltage substation is between 50%~95%, and the simultaneous coefficient of the two transformers in the high voltage substation is about 1. The test results show that the power supply reliability of the high voltage substation tested is high, and the power supply capacity of the high voltage substation is still relatively large due to the short operation time of the high voltage substation.