Abstract: The injection of CO₂ into geologic bodies, such as oil reservoirs and coalbed, can enhance the recovery of oil and gas, also has the potential of storing large volumes of CO₂. The storage of CO₂ can be acquired by calculating carbon dioxide's volume by its different phases in the geologic bodies. Thus, the specific contribution of each phase can also be gained with the total storage ability of geologic body. The storage of CO₂ in coal seam is divided into absorpton, free and dissolved three parts according to each of its phases. The increase of storage capacity led by the increase of pressure, the expansion of pores, is also considered. According to the calculation, the amounts of gaseous amount, amount of dissolved and incremental expansion led by inflation are all increased in pace with the increase of injection pressure, so are the percentages of the last three parts. The fraction of absorbed CO₂ can be as high as 90%.