Abstract: According to the difficult problem that gas loss quantity of coal seam is difficult to accurately calculate during the sampling measurement, the gas desorption process simulation test is made under adsorption equilibrium absolute gas pressure 1.5 MPa, experimental temperature 20 ℃ and 1-3 mm size coal sample in the laboratory. Using SPSS software to regress the test data, the analysis results show that the index model can not only describe gas desorption process, but also can predict gas loss quantity and established gas loss quantity prediction model during sampling. According to the established model and experimental data, it is concluded that the model of the gas loss quantity calculation error is less than 10% when exposure time is less 3 min. Using the model of gas loss quantity calculation, sampling time should be controlled in 3 min. Through validating the model with the data of laboratory and field test, the result shows that the error of the model of the gas loss quantity during sampling is 1.68%-10.97%, and the average error is 6.98%. The result can meet the engineering needs.