In order to optimize the working performance of air source heat pump air conditioning system and realize the efficient use of energy, this paper researches on its optimal working conditions, introduces and designs the experimental system and experimental scheme, researches on the temperature control strategy based on the two types of water return methods: fixed return and variable return, and analyzes the different working conditions of the two types of control strategy in terms of the four indexes: refrigeration capacity, unit loading rate, COP, and the power consumption of the unit. The study also analyzed the different working conditions of the two control strategies in terms of four indicators: cooling capacity, unit load rate, COP, and unit power consumption, and concluded that the optimal operating condition is the one in which the whole terminal is turned on in the variable return water temperature.