In this study, a one-step method of polyethylenimine (PEI) cross-linking graphene oxide (GO) was used to prepare a 3D pore-structured adsorbent with abundant amine groups for chemisorption of CO2. The cross-linking of PEI with GO sheets and the vacuum freeze-drying step are the keys to the formation of the 3D pore structure. The results of characterization analysis revealed that the as-prepared adsorbent had a 3D porous structure rich in amine groups. Besides, the adsorption/desorption test showed that the prepared adsorbent has excellent and stable adsorption performance, and the maximum CO2 adsorption capacity is 2.18 mmol/g at 343 K and 10 vol % CO2. Moreover, the adsorption kinetics analysis indicated that the adsorption process was dominated by homogeneous adsorption, and the adsorbent had a strong affinity with CO2. Finally, the correlation analysis shows that the kinetic constants obtained by the Avrami model simulation can be effectively used for the actual CO2 adsorption process design.