Active neutral point clamped (ANPC) inverters are characterized by low output waveform distortion rate and high transmission efficiency, and have been wide use, but a large numbers of switching devices reduce the reliability of the inverter. The current path of a threelevel ANPC inverter under different opencircuit faults of switching devices is analyzed, and the output level and output voltage space vector changes under different faults are obtained. Combining the relationship between the midpoint current and the output current under the action of each vector, a fault diagnosis method based on the midpoint current is proposed. According to the characteristics of the ANPC inverter circuit, different faulttolerant modes are proposed for its bridge arm devices and clamp devices, and a faulttolerant circuit structure with nonderating fault tolerance is proposed. The proposed fault diagnosis method and faulttolerant strategy are verified by building a simulation model and experimental platform. The simulation and experimental results show that the fault diagnosis method and faulttolerant strategy are feasible.