Abstract: External air leakage ratio was one of important indexes to measure running status of main fan and ventilation management level in coal mine, and the selection of measurement methods was the chief issue for the field technique personnel when measuring external air leakage. According to coal mine ventilation principle, it analyzed the principle, process, and application condition for various measurement methods of external air leakage. Through taking external air leakage measurement of Wugou Coal Mine as the example, it discussed the basis and process of the methods selection. The field test results showed that external air leakage ratio was 8.4% and 7.85% respectively corresponding 1^# fan and 2^# fan running, the equipment air leakage of spare fan was the primary air leakage fountainhead, so specific measures must be applied to control air leakage. The test results provided scientific field reference for eliminating air leakage hidden trouble and optimizing coal mine ventilation system.