The main risks of prepositive tandem air-cooled heat recovery system were adequately analyzed,and a refrigerant control strategy applied in this type of unit was raised to resolve these risks.The test data prove that the operation situation of an air-cooled heat recovery chiller unit is stable in normal conditions,and can be significantly improved in condition that the inlet hot water temperature is 30 ℃:the sub-cooling is increased from 0.2 ℃to 3.1 ℃; the heat recovery rate of the unit condensing heat is increased from 16.34% to 19.48%,and the heat recovery leaving water temperature is increased by 2.5 ℃.When the discharge pressure of the compressor is too high,the control system can recycle the redundant refrigerant in system to ensure the unit's stable operation according to the control logic.By using the refrigerant control strategy proposed,the root problems of prepositive tandem air-cooled heat recovery system can be solved.