An amphiphilic PEI-g-OA copolymer (PEI-OA) was synthesized by Michael addition reaction between branched-polyethyleneimine (B-PEI) and octadecyl acrylate (OA), and then introduced into the concentrated emulsion as macromolecular emulsifier. A amine-loaded polystyrene (PS) porous polymer, which could be used as solid CO2 adsorption material, was prepared one-step via emulsion templating method. The effects of the macromolecular emulsifier, addition of emulsifier, and volume fraction of dispersed phase of concentrated emulsion on the micro morphology and then CO2 adsorption capacity of the porous polymers studied. The result shows that the synthetic PEI-OA emulsifier tends to form O/W emulsion, and a porous structure constructed by dense particles was obtained. The porous channels could be controlled by the addition of emulsifier and dispersed phase volume fraction of concentrated emulsion. The CO2 adsorption capacities of amine-loaded porous polymers were measured by gas adsorption analyzer. The results indicate that the increase of PEI content, emulsifier addition, and dispersed phase volume fraction would improve the CO2 adsorption capacity, and the maximum adsorption capacity of 2.65 mmol/g is achieved. Moreover, the cyclic test result shows that the adsorption capacity decreased by only 0.15% after 5 cycles. It is concluded that the porous polymer as-prepared amine-loaded CO2 adsorption material has a good industrial application prospect.