Calculation of refrigerant quantities in the heat-exchangers of an air-conditioner on refrigeration and heating operating conditions shows that refrigerant charge quantity in heating operating condition is less than that in refrigeration operating condition. The refrigerant control strategies are most important for refrigeration and heat-pump system. Based on the difference of charged refrigerant quantities of the air-conditioning system between refrigeration and heating operating conditions, the exhaust bypass method was presented in order to improve its operation efficiency. This heat-pump system for controlling refrigerant mass flux was analyzed in detail. The results show that the exhaust bypass method has its advantages in controlling refrigerant mass flux for heat-pump system.