This paper describes the isothermal desorption chracteristics of mixed CH4/CO2 gas for the Late Paleozoic Coals with different ranks from the Kailuan Coalfield, Hebei Province. The abundance and variation of each gas in adsorption phases were analyzed using the extendedLangmuir equation. The results of isothermal desorption experiments show that the mediumrank coal (Ro= 1.21 %) has a stronger adsorption ability of the mixing gas than the lowrank coal (Ro= 0.58%). The quantity of the adsorbed mixed gas by the coal increases with the increasing of the CO2 quality in the mixed gas. The relative abundance of CH4 in adsorbed phase decreases and that of CO2 increases gradually with desorption. As compared to the lowrank coal, the mediumrank has a higher unit desorption rate for CH4. The replacement of CH4 with CO2 will be more efficient when more quantity and higher relative abundance of CO2 is injected. The mediumrank coal is more subjected to be used for CO2 Sequestration and Enhanced Coalbed Methane technique than the lowrank.