Abstract: Deep coalbed methane (CBM) resources are abundant in Daning-Jixian block in the eastern margin of Ordos Basin, and the development practice in recent years has broken through the traditional understanding that it is difficult to develop and utilize deep CBM resources. At present, there are still a series of geological problems unsolved in the exploration and development of deep CBM, and especially the control factors of gas-bearing properties and the prediction of free gas content seriously restrict the resource evaluation and efficient development of deep CBM. Comprehensively using the geological data of CBM development and experimental testing methods, the paper compares and analyzes the differences in gas content between mid-deep coal seams (with buried depth from 1 000 m to 1 500 m) and deep coal seams (with buried depth greater than 1 500 m) in Daning-Jixian block, thus discovering the internal and external controlling factors of gas content in deep coal seams, and establishing the prediction models and vertical distribution patterns of gas content in different phases. The results show that the gas oversaturated coal reservoirs are generally detected in deep layer, of which the free gas proportion is from 17% to 43% and tends to increase with reservoir pressure. The free gas content is negatively correlated with water saturation. Before adsorption and saturation, coal reservoir pressure can promote the adsorption of methane by coal seams, while temperature and moisture can inhibit the adsorption of methane. Compared with low-rank coal, high-rank coal has stronger methane adsorption capacity, which is mainly attributed to the material composition of coal, pore structure, physical and chemical reactions between methane molecules and coal surface. Due to many limitations, the adsorbed gas content in coal seams presents a changing trend from "rapid rise to slow growth to slow decline" with the increase of buried depth, while the free gas content presents a trend from "stable rise to slow growth to being constant". Therefore, the change of total gas content in coal reservoirs with buried depth is divided into four evolution stages:rapid rise, slow rise, remaining stable and slow decline.