Abstract: It is necessary to build up the correlation of the aerosol leakage rate with the gas leakage rate for evaluating aerosol leakage of nuclear facilities. The method of evaluating leakage rate of gas and sub-micron aerosol was summarized and also investigated by experiment. The effects of upstream aerosol number concentration, flow velocity and upstream pressure on aerosol leakage were analyzed based on the experimental results. The results show that the aerosol leakage rate is linearly related to the gas leakage rate in capillary when the gas leakage rate is higher than 10^-4Pa·m³·s^-1; the aerosol leakage rate falls sharply due to the diffusion deposition mainly for sub-micron aerosol when the gas leakage rate is lower than 10^-4Pa·m³·s^-1. The aerosol leakage rate is explored to be expressed as a function of the gas leakage rate and the orifice length under some certain assumptions for practical application.