The invention discloses a defrosting control device and a defrosting control method of a heat pump air conditioner. A humidity sensor for collecting the humidity RH of the outdoor environment outsidethe automobile; The defrosting controller is configured to determine a frosting mode of the heat pump air conditioner according to the outdoor ambient temperature T1 and the outdoor ambient humidity RH, and perform a corresponding defrosting operation according to each frosting mode. The heat pump air conditioning defrosting device and method of the invention collects the outdoor ambient temperature T1 and the outdoor ambient humidity RH, The frosting mode of the heat pump air conditioner is determined, and corresponding defrosting operation is carried out according to each frosting mode, so as to accurately defrost according to different frosting modes, and the defrosting is realized without reverse circulation in all environments, so that the system structure is simplified, the defrosting efficiency is improved, and the comfort of occupants is improved.