Heat pump air conditioner system and control method thereof

The invention provides a heat pump air conditioner system and a control method thereof. When the air conditioner system runs in a heating mode, to prevent an outdoor heat exchanger from being frosted,the heat pump system achieves defrosting running through reversing of a four-way valve. During defrosting running, to guarantee indoor comfort, indoor heat supply is guaranteed in the manner of additionally mounting electric heaters. In the heating defrosting process of the air conditioner system, room temperature fluctuation caused by defrosting in the heating process is reduced by controlling switches of a first evaporator, a second evaporator, the first electric heater, the second electric heater, a first evaporation fan and a second evaporation fan, meanwhile, the defrosting time can be prolonged, defrosting of an outdoor unit is achieved more thoroughly, the situation that after the system enters the heating mode again, the heat exchange effect is influenced due to the fact that theoutdoor unit is frosted is