Coal-fired power plants are producing flue gas including almost of Nitrogen (around 79%), next is Carbon dioxide (around 10-15%), and small amount of others gases such as H2, NOx, SO2. One of the promising methods to reduce CO2 emission is the CO2 sequestration into deep un-mineable coal seams. Presently, the flue gas exhausted from coal-fired plant must be separated to get pure CO2 before injecting into coal seams. In order to enhance the efficient of Carbon Capture and Storage (CCS) from coal-fired power plant, the oxyfuel combustion technology has been expected. This technology using pure oxygen to combust the coals, therefore, CO2 concentration in the flue gas is increased up to 95% theoretically. This study aimed at characterizing CH4 replacement mechanism in coal by using pure CO2 and a synthesis flue gas (99% CO2 and 1% SO2) that is similar with emission gas from the plants. A measurement procedure for gas adsorption is that after getting methane adsorption equilibrium of the coal samples, pure CO2 or the synthesis flue gas is injected into an adsorption cell in order to investigate CH4 replacement properties. Coal samples used for present experiments were taken from coal seam No 9D, Maokhe coal mine, Vietnam. It was crushed with the size from 250μm to 2mm. The concentration of gases was taken from the adsorption cell and analyzed by using a gas chromatograph. Adsorption isotherms of CH4, CO2 and SO2 were measured by using the volumetric method apparatus. The characteristics of methane replacement by using pure CO2, the synthesis flue gas and effect of SO2 on adsorption properties of coal have been discussed in this paper.