Abstract: For the sake of easily damaged characteristic of active power filter（APF）,proposed a low-cost,open-circuit fault diagnosis and fault tolerant control program based on hardware circuit.Open circuit fault diagnosis and fault-tolerant control hardware circuit rapidly diagnose and identify the source of the fault,generate a fault-tolerant control signal,control relay and drive AC contactor to remove the fault,switch failure phase to the midpoint of DC side capacitor,change the APF to three-phase four-switch topology.Controller would switch control algorithm according to the diagnostic circuit signal.Analyzed the characteristics of space vector of every kind of open-circuit fault,provided a basis of how to switch control algorithm for the controller.The experimental results showed that the hardware open circuit fault diagnosis and fault-tolerant control scheme achieved the expected control effect.