Abstract: By testing hydrocarbon isotopes of gas samples taken at the site, the composition of carbon and hydrogen isotopes and differences with δ13C(CH₄), δD(CH₄) and δ¹³C(CO₂) in a single coal seam gas and multiple mixed gas of coal seam are analyzed, and the close coal seams are compared and analyzed. The mathematical method is used to set up the model and the mixed hydrocarbon isotope characteristics of gas from different sources are used to establish a calculation formula of mixed gas isotopes. Through testing the numerical value of isotope which is in a single coal seam gas and multiple mixed gas of coal seam, the proportion of different gas sources is analyzed and calculated, and a model of multiple source gas is builded. The source and proportion of each coal seam gas in the gas sample are determined. Through researching the gas source of XV1306 working face of 15^# coal, the proportion to the gas sample of different gas sources is analyzed and calculated in order to provide the basis for gas source and governance in XV1306 working face. The method of differentiating source drainage is used to ensure the safety of working face and efficient production.