The invention relates to a heat pump clothes drying system and a clothes drying method thereof. The heat pump clothes drying system comprises a heat pump evaporator unit, a heat pump compression condensing unit and a drying chamber. A refrigerant loop of the heat pump evaporator unit is connected with a refrigerant loop of the heat pump compression condensing unit through a refrigerant pipe. An air path outlet of the heat pump evaporator unit is connected with an air path inlet of the heat pump compression condensing unit through a pipeline, an air valve A and an air valve C are sequentially disposed on the pipeline in parallel, and an air valve B is disposed on the pipeline between the air valve A and the air valve C. An air path outlet of the heat pump compression condensing unit is connected with an air path inlet of the drying chamber. An air path outlet of the drying chamber is connected with an air path inlet of the heat pump evaporator unit through a pipeline, an air valve F and an air valve D are sequentially disposed on the pipeline in parallel, and an air valve E is disposed on the pipeline between the air valve F and the air valve D. By the heat pump clothes drying system, clothes drying quality is guaranteed while energy consumption is reduced maximally, and drying speed is increased.