In view of the open circuit fault diagnosis of threephase inverter, a fault diagnosis method based on residual theory with dynamic reference quantity is proposed. This paper is to utilize the existing phase voltage sampling signal of the inverter closedloop control system, take the phase voltage waveform with one period delay as a dynamic reference, and obtain the voltage residual waveform by comparing the dynamic reference voltage signal with the current phase voltage signal through setting a reasonable fault detection threshold for realizing the accuracy diagnosis of the open circuit fault of the inverter. The simulation results show that this method has the ability to resist unbalanced load and the load mutation interference, and the diagnosis time is less than one cycle, and has the advantages of low complexity and easy implementation.