A discharging method of a bus capacitor, a controller, a DC-DC converter and an inverter are provided. After a DC-DC converter or an inverter is powered off, in a case that a detected voltage across a bus capacitor of the DC-DC converter or the inverter is determined to meet a preset condition, a switch of the DC-DC converter or the inverter is controlled to be turned on or turned off to cause the bus capacitor, the switch, and a reactor of the DC-DC converter or the inverter to form a current loop, until the voltage does not meet the preset condition. Based on the method, discharging function is achieved for the bus capacitor after the DC-DC converter or the inverter is powered off, without the need for an additional discharging circuit, which solves problems caused by the additional discharging circuit required in the conventional technology.