The invention provides a defrosting control method with the optimal comprehensive performance of an air heat source pump as a target. The defrosting control method comprises the steps that when a unit is started, the evaporation pressure/temperature, the inlet air temperature and the inlet air humidity of a finned tube exchanger and the condensation pressure/temperature and hot water side inlet temperature and flow of a condenser are detected, performance parameters of different running periods are calculated through a unit model in a simulation manner, and the optimal unit frosting time under the work condition is obtained according to the calculated maximum value of the performance evaluation coefficient COPc of the different running periods; when the unit carries out heating and runs to the optimal frosting time, defrosting is started; and the temperature of bottom fins of the finned tube exchanger is detected, and when the temperature of the bottom fins of the finned tube exchanger reaches the set value, the unit stops defrosting, and the heating mode is recovered. According to the defrosting control method, the running work condition and the running state of the unit are detected in real time, the growth condition of a frosting layer of the finned tube exchanger can be accurately judged through the unit model, the optimal frosting time of the unit is updated, and the unit can adapt to any work condition to efficiently run.