Abstract: The available data show that the gas content of low-rank coal is generally low at the depth less than 1 000 m, however, the pilot production of gas of deeper low-rank coal has better effect. Based on the Langmuir equation, we carried out the low-rank coal isothermal adsorption simulation experiments under high temperature and high pressure. The experiment results show that the adsorption capacity of brown coal was the weakest, about a third of long-flame coal and gas coal, and adsorption quantity increased gradually with coal rank; the experiments results also show that the adsorption quantity of low-rank coal increased rapidly under 55℃ and 12 MPa, with the increase of temperature and pressure, the mathematical model for the process was established based on temperature-pressure-coal rank; the adsorption quantity present the trend of fast increase-slowly increase-slowly decrease with the increase of buried depth. There exists a critical depth belt for adsorption quantity, ranging from 1 400 m to 1 700 m. At the depth less than 1 400 m, the positive effect of pressure for the adsorption quantity was greater than the negative effect of temperature, the adsorption quantity increased with the buried depth, reached the limit in the critical depth belt and increased no longer. The negative effect of temperature was greater than the positive effect of pressure at depth more than than 1 700 m, the adsorption quantity decreased with depth. The experimental results provided the theoretical basis for assessment of CBM resources and the development potential of deep low rank coal.