The invention discloses an air conditioner control method, device and system and a controller. The air conditioner control method comprises the steps that the set temperature of an air conditioner is obtained, and the outdoor temperature, the indoor temperature, the sunlight illuminance and the surface temperature of an evaporator are acquired; the target temperature of an air outlet is determined according to the set temperature of the air conditioner, the indoor temperature, the outdoor temperature and the sunlight illuminance, and the target temperature of the evaporator is determined according to the target temperature of the air outlet; the current control voltage is determined according to the target temperature of the evaporator, the surface temperature of the evaporator, the target temperature, obtained in the previous acquisition cycle, of the evaporator, the surface temperature, obtained in the previous acquisition cycle, of the evaporator, and the output voltage obtained in the previous acquisition cycle; and the discharge rate of a compressor is controlled according to the current control voltage. According to the air conditioner control method, device and system and the controller, automatic control over the displacement of the compressor is achieved, the control accuracy of the surface temperature of the evaporator is improved, the opening and closing frequency of a clutch is reduced, and the energy utilization rate is increased.