Provided are a fuel supply device and an oil discharge mechanism thereof. The fuel supply device comprises a body, and a fuel supply mechanism and a lower cover installed on the body. The bottom of the lower cover is provided with an oil discharge mechanism. The oil discharge mechanism comprises an oil discharge handle, an oil discharge pin roll, an oil discharge shaft sleeve, and an oil discharge spring. The oil discharge handle comprises a handle body and at least a bulge extending along one side of the handle body. The oil discharge pin roll is installed in an oil discharge hole. The top end of the oil discharge pin roll is connected with the oil discharge handle, and the bulge is on the outer peripheral surface of the oil discharge pin roll. The oil discharge shaft sleeve is sleeved on the oil discharge pin roll and is on the outlet of the oil discharge hole. The end of the oil discharge shaft sleeve, close to the oil discharge handle, is provided with a groove matched with the bulge. The oil discharge handle is provided with a sealing position and an oil discharge position relative to the oil discharge shaft sleeve. The oil discharge spring is sleeved on the oil discharge pin roll. Two ends of the oil discharge spring are respectively abutted between the other end of the oil discharge shaft sleeve and the tail end of the oil discharge pin roll.