Abstract: Leaking safety is an issue preventing air conditioner using R290 from being widely used, and ventilation is an effective method to improve leaking safety of integral-type air conditioner. In this paper, the concentration of leaking refrigerant of integral-type fresh air air conditioner was studied experimentally, combined with CFD simulation, and the leaking safety was evaluated. Results show that due to the dilution of supply air flow, in the location with highest concentration, namely supply air outlet, no higher concentration than LFL is monitored. However, there still exists the possibility of combustible region in the indoor unit. Moreover, fresh air contributes to remarkable decrease of refrigerant concentration after leakage with a decrease rate as high as 15.6% LFL/h. Therefore, the main research spot should be fixed on the prevention of ignition source inside the indoor unit. This paper is helpful for having a knowledge of leaking rules of integral-type fresh air air conditioner and provides a reference for the design of air conditioner using flammable refrigerants.