A fault detection method is used to determine whether a power switch coupled to a DC bus of a power conversion circuit is faulted. The method includes: detecting a bus voltage to provide a voltage signal and acquiring at least one detection value according to the voltage signal; providing control signals sequentially to turn off or turn on the power switch; determining that the power switch is a short-circuit fault if a first detection value is greater than or equal to a first threshold value when the power switch is turned off; determining that the power switch is an open-circuit fault if a second detection value is less than a second threshold value when the power switch is turned on; and providing an alarm signal or a disable signal when the power switch is the short-circuit fault or the open-circuit fault.