Since switching device faults are the main type of faults in active neutral point clamped (ANPC) three-level inverters, quickly locating the faulty devices is of great significance to improve the reliability of ANPC three-level inverters. For open-circuit faults of switching devices in ANPC three-level inverters, the impact of switching device faults on output current under different modulation algorithms and the influence of the phase difference between output current and load-side voltage on fault current waveform are analyzed from the perspective of propagation paths. Using the three-phase output current as the fault characteristic quantity, an open-circuit fault diagnosis method for ANPC three-level inverters based on switching modulation strategy is proposed. The current averaging method is used to initially determine the approximate range of the faulty switching device, and then the switching modulation strategy is used to precisely locate the faulty device. Finally, simulations and experiments verify that the method can locate faults within one fundamental waveform cycle, with advantages of fast detection speed, strong anti-interference ability, and no need for additional sensors for fault detection.