Abstract: In order to solve the problem that in the process of measuring the external air leakage rate of return shaft type mine by tracer gas method, the limited length of the main return air roadway may lead to the inaccuracy of tracer gas sampling and detection, taking the No.1 return air shaft and No.2 return air shaft of Nalinhe No.2 mine as the research object, the test scheme of tracer gas method for the external air leakage rate of multiple return air shaft is established.On this basis, the shortest sampling distance of SF₆ gas in each main return air roadway is calculated by theoretical formula method and CFD numerical simulation method respectively.The calculation results of theoretical formula method show that the tracer gas method is not suitable for measuring the external air leakage rate of No.1 return air shaft and No.2 return air shaft, and the results of CFD numerical simulation are opposite.The field measurement results show that the SF₆ gas distribution in the roadway section at the shortest sampling distance of the return air roadway determined by the CFD numerical simulation method is uniform, and the accuracy of the CFD numerical simulation method is significantly greater than that of the theoretical formula method.The research show that calculating the shortest sampling distance of the tracer gas by the CFD numerical simulation method could be used to demonstrate scientifically and accurately field applicability of the external air leakage rate of return shaft type mine by tracer gas method.