The invention relates to a porous activated carbon material capable of efficiently adsorbing CO2 and a preparation method of the porous activated carbon material. The preparation method includes the steps of firstly, evenly mixing biomass serving as the carbon source with an activating agent, and grinding to obtain raw material powder; secondly, calcining the raw material powder obtained in the first step under certain atmosphere at 500-1000 DEG C for 30 minutes to 10 hours, cooling along with a furnace, taking out a sample, cleaning the sample with deionized water, and drying to obtain the porous activated carbon material capable of efficiently adsorbing CO2. The porous activated carbon material and the preparation method thereof have the advantages that the biomass is used as the carbon source, and low cost and environment friendliness are achieved; the carbon source and the activating agent are blended and carbonized and activated in one step to obtain porous activated carbon, and simple process and simple operation are achieved; the CO2 adsorption capacity of the porous activated carbon material under normal temperature is increased evidently, and the material is excellent in CO2/N2 selective adsorption performance.