With the rapid development of urban subway system in recent years, the failure of subway traction network has become a research hotspot. In order to ensure the reliability of the subway power supply, better study the fault characteristics, provide close to the real subway short circuit current, study the action characteristics of the subway high voltage DC circuit breaker under the fault current, design a simulation device based on phase shift full bridge that can generate the subway short circuit current, by controlling the amplitude, frequency, initial phase angle of the input waveform, so that the corresponding waveform can be generated. And it is verified by experiments. The experimental results show that the output has the characteristics of good dynamic response and small error. Considering that the sensor is affected by the interference noise such as the environment, the Luenberger observer is added to optimize the device control algorithm reasonably.