Abstract: Whether the calculation of gas loss amount is accurate or not, it directly affects the results of determination of gas content. Through analyzing the mathematical model that calculated from gas loss quantity, sampling method, coal desorption performance and other aspects, the paper determines that the coalbed gas desorption is the result of multiple factors dynamic coupling effect, and it should be selected based on the actual situation of the mathematical model. To reduce the influence error of gas loss amount, the exposure time of coal body should be as short as possible and maintain the integrity and tightness of the coal core.