The differences of Coalbed Methane（CBM） geological characteristics and gascontrolling function between low rank coal and high rank coal, which is an important portion of the CBM reservoir research and the CBM development and exploration theory research. Based on some CBM basins, such as Qinshui, Fuxin and Power River Basin in America, physical property differences of reservoirs between high and low coal ranks were discussed, gascontrolling differences between structure and hydrologic geology were analyzed. The reservoirs with the high rank coal have high gas content, with δ13C1 value over -38.75‰, poor permeability. Reservoir reformation is difficult. Tectonic thermal event contributes mainly to CBM generation and enriching. Everlasting hydrodynamic force would destroy CBM reservoir seriously. The reservoirs with the low rank coal have low gas content, with δ13C1 value <-49.11‰, good permeability. Reservoir reformation is comparatively easy. CBM generation and enriching are influenced by coal thermal evolution history and coal rank. During the CBM generating process, stirring hydrodynamic force is taken as the main geological agent, but everlasting hydrodynamic force would destroy CBM reservoir slightly, and proper formation water salinity is an important factor of low rank CBM generating.