Abstract: CBM Adsorption/Desorption data are the key parameters to appraise CBM resources and productivity. The current conventional Isotherm adsorption experiment can only provide the relationship between adsorption volume and pressure at a fixed temperature set at the beginning of experiment. How to get the real adsorption/desorption data in the in-situ condition become a challenge for the CBM laboratory. To overcome the bottlenecks existing in isothermal CBM adsorption testing which currently adopts the US5058442/4528550 patent and IS-300 insitu absorption instrument, such as small testing scope, damage of sample^’s original structure, and free from restraint by surrounding pressure, Langfang CBM laboratory created a new CBM adsorption/desorption simulation device that overcomes the shortcoming that the current in-situ adsorption testing does not take into account the influence of stress and cannot reflect the real adsorption status of the formation. Particularly, the method for in-situ adsorption testing of non-adsorptive gas provides the parameters for calculation of variable volume free space. Successful development of this instrument localizes the isothermal adsorption apparatus and creates the in-situ CBM adsorption simulation under the high-temperature condition. The research indicates that the effect of high temperature on CBM adsorption capability is higher than that of pressure under the conditions of high temperature and pressure (>85℃ , >30MPa), thus confirming that a ^“critical depth^”exists in the relationship between CBM content and buried depth. Namely the CBM content in the shallow layer increases with the rise of buried depth and reaches the maximum value at a certain buried depth. Then the CBM content decreases with the further rise of buried depth after exceeding the certain depth.