The invention discloses a compressor protection device used when an air conditioner lacks fluorine. The compressor protection device comprises an indoor ambient temperature sensor, a first temperature sensor, a second temperature sensor and a control unit, wherein the first temperature sensor is arranged at the inlet of the evaporator of the indoor unit of the air conditioner, and the second temperature sensor is arranged on the middle coil of the evaporator of the indoor unit of the air conditioner. The control unit comprises a comparator, a timing unit and an actuating mechanism used to cut off the power supply of the air conditioner. When the temperature detected by the second sensor is 7-9 DEG C larger than the temperature detected by the first sensor or the temperature detected by the indoor ambient temperature sensor is 2-4 DEG C less than the temperature detected by the first sensor, the timing unit is started up to start to time and the actuating mechanism cuts off the power supply of the compressor within 28-32 seconds after timing. Since the compressor is protected when the air conditioner lacks fluorine through the variation of the difference among the temperature of the inlet of the evaporator, the temperature of the middle coil of the evaporator and the indoor ambient temperature, the invention has the advantage that the protection of the compressor is realized at low cost when the air conditioner lacks fluorine.