Abstract: In order to forecast gas absorption of reservoir with CO2 flooding, and provide theory basis for CO2 injection alloca-tion rate and relevant parameters optimization design, on the basis of previous studies, the physical model and mathematical model were established for two-dimensional CO2 miscible slug flooding. Taking the effect of miscible slug on injection process into account, theoretical derivation was conducted to obtain the calculation model of gas absorption capacity for CO2 miscible flooding. Simulation calculated results show that the relationship between CO2 injection pressure and injection velocity are approximate linear, and the bigger the injection pressure, the higher the injection velocity. Formation pressure is in stair distribution, and presents three different pressure gradients. The pressure drops in supercritical CO2 region and miscible phase region is relatively low, which means that the pressure mainly was consumed in crude seepage area. Gas absorption ability enhances as the cumulative injection quantity and the miscible slug length increase. Gas absorption index presents a logarithmic type growth with rise of the cumulative gas injection volume and will grow linearly with the slug length increase.