The invention relates to the field of PFC control, and discloses a PFC circuit control method and device, a PFC circuit and a motor drive circuit. A bus reference voltage is generated by acquiring a reference current and voltage based on a two-phase rotating coordinate system and generated by a controller, a bus voltage output by the PFC circuit is acquired to determine a boost ratio coefficient,and then an input current of the PFC circuit is acquired to determine an input average current, to determine a duty ratio of a switching tube that drives the PFC circuit, and finally according to theduty ratio, the switching tube is controlled to perform a switching operation to control the operation of the PFC circuit. In this way, the boost ratio coefficient changes with the bus reference voltage and the bus voltage, which can ensure the reasonable setting of a set-up ratio coefficient in an ultra-low voltage environment; and finally the switching tube of the PFC circuit is controlled to operate according to the duty ratio determined according to the set-up ratio coefficient, to obtain a reasonable bus voltage. Therefore, it is ensured that the motor drive circuit is in a proper state to ensure that devices in the circuit are safe and are not damaged.