The invention discloses a washing method of an air conditioner. The washing method comprises the steps: S1, dewing is conducted, specifically, refrigeration is conducted to form condensate water for primary washing; S2, frosting is conducted, specifically, refrigeration is conducted to form a frost layer; S3, heating is conducted, specifically, heating is conducted to defrost to washing the surface of a heat exchanger, and sterilization is conducted; and S4, ventilating is conducted, so that the heat exchanger is quickly dried and cooled. The air conditioner comprises a control device, and operations of the rotating speed of a fan and the operating frequency of a compressor of the steps are preset in the control device, wherein the preset operation in the step S3 is that the mapping relation between the pipe temperature T of the heat exchanger and the frequency of the compressor and the mapping relation between the environment temperature and the rotating speed of the fan cooperate tocontrol the pipe temperature of the heat exchanger. According to the washing method, on the one hand, two-step cleaning is achieved, and sterilization is conducted; on the other hand, a system of theair conditioner is utilized to the largest extent; and secondly, through setting of the heating stage, the problems that under the high-temperature working condition, the operating frequency is too high, the air speed is too low, the pipe temperature rises too quickly, when frequency decreasing is triggered, the pressure is too high, and compressor driving protection occurs are avoided.