The invention discloses a detection method and system for leakage of a refrigerant of an air conditioner. The detection method comprises the steps of S10, acquiring the current running mode of the air conditioner, the current temperature of the outdoor environment and the current temperature of the indoor environment; S20, searching the normal refrigerant mass flow rate Q; S30, acquiring the current suction temperature tsuction and the suction pressure Psuction of a compressor; S40, searching the current suction specific volume Vsuction of the compressor; S50, calculating the current refrigerant mass flow rate QM; S60, judging whether the current refrigerant mass flow rate QM is smaller than the normal refrigerant mass flow rate Q; S70, if QM is smaller than Q, calculating the decrease percentage eta according to the formula that eta equals to (Q-QM)/Q%; and S80, comparing the eta with a preset percentage threshold value X. According to the detection method for leakage of the refrigerant of the air conditioner, the detection steps are decreased, the transmitted data is decreased, and accordingly detection faults are avoided, and the method is simple and reliable.