The invention provides a PG motor control method and device and an air conditioner, and relates to the technical field of air conditioners. According to the method and device, a power supply voltage frequency is obtained, a theoretical zero passage interval time of a zero passage signal is calculated on the basis of the power supply voltage frequency, a practical rotation speed value of a PG motoris obtained at the same time, a conduction parameter of the PG motor is determined on the basis of the practical rotation speed value and the theoretical zero passage interval time, and the operationof the PG motor is controlled on the basis of the conduction parameter. The conduction parameter is adjusted through the power supply voltage frequency and the practical rotation speed value of the PG motor, namely, a practical conduction pulse width and a practical delay time are adjusted, so that the condition that the practical conduction pulse width is small and the practical delay time is large is avoided, and enough conduction pulse width exists for control when current zero passage lagging voltage passes the zero under the condition that the load of the PG motor is relatively heavy, thereby ensuring the effective time of the conduction pulse width and avoiding the stall condition of the motor.