The invention discloses a heat pump air conditioner, which includes an outdoor unit, an indoor unit, a gas pipe and a liquid pipe, the outdoor unit and the indoor unit are connected through the gas pipe and the liquid pipe, the indoor unit includes a casing, and the casing is provided with an air inlet and an outlet. In the air outlet, an indoor fan, an indoor heat exchanger and an electric heater are arranged in the casing, an air inlet grille for closing or opening the air inlet is arranged on the air inlet, and a grille for closing or opening the air outlet is arranged on the air outlet. Air outlet grille, when the air conditioner reverse cycle defrosting, the control will turn on the electric heater, and drive the air inlet and outlet grille to close the air inlet and outlet, so that the air inside the cabinet is isolated from the indoor air. Driven by the fan, the circulating air can quickly transfer the heat generated by the electric heater to the low-temperature refrigerant through the finned tube heat exchanger, which can not only quickly remove the frost, but also prevent the low-temperature refrigerant from absorbing heat from the room , improve indoor comfort, and apply the present invention can also improve the dehumidification effect of the air conditioner.