Abstract: In the surroundings of the Gaoqing-Pingnan fault zone five CO2 gas reservoirs are developed. Based on the data on compositions, isotope geochemistry and CO2/3He of the reservoirs, it is shown that CO2 distributed in the Gaoqing area was mostly originated from the mantle-sourced inorganic material associated with magmatic rocks. The 3He/4He ratios range in 2.02×10-6~8.34×10-6 and 40Ar/36Ar ratios range in 628.9~3178. The higher 3He/4He and 40Ar/36Ar ratios in CO2 gas pools prove a major mantle-magmatic origin of the noble gases, with a part of crustal source gas mixed. The average 4He/40Ar* of 2.15 shows a slow degassing rate of magma. Its formation mechanism can be interpreted as follows: During the magma rising, the pressure and te perature would decrease, the magma composition would change, and the solubility of CO2 and noble gases in magma would also decrease. Consequently, the CO2 and noble gases could be separated from the magma, and large amount of CO2 and rare gases could be transported to the various stratigraphic traps along the deep faults and some second- and third-order faults.