To investigate the coadsorption of SO2, NO, and CO2 from the flue gas, adsorption equilibrium tests of SO2, NO, and CO2 on coconut shell activated carbon (SAC) and coal-based activated carbon (CAC) were conducted at the temperatures (323, 343, and 363) K by the static volumetric method. The equilibrium data were well fitted by the Toth model. Henry's constant was calculated by the Virial model; the results showed that adsorption affinity followed the order SO2 > CO2 > NO > N-2 on SAC, and SO2 > NO > CO2 > N-2 on CAC. Then thermodynamics data, including Gibbs' free energy, entropy, and enthalpy, were also calculated to characterize adsorption behaviors. SO2 had the highest degree of freedom, while CO2 formed a most regular configuration. The efficiency of molecule packing in CAC was lower than that in SAC. Finally, competitive adsorption of different flue gas components was predicted by the extended Toth model. The adsorption amount followed the order CO2 > N-2 > SO2 > NO for both adsorbents. SAC had better adsorption property than CAC in the multicomponent adsorption.