The invention discloses a solid absorbent with high CO2 adsorption capacity and a preparation method thereof. The solid absorbent comprises active components and a carrier; the active components are alkali carbonate and an amino group at the surface of the carrier, and are 15-60% of total quality of the solid absorbent; the molar ratio of the alkali carbonate and the amino group is 1 to (0.5-25); and the carrier is monox, and is 40-85% of total quality of the solid absorbent. The preparation method comprises the following steps of mixing and stirring the materials into emulsion; putting the emulsion into air to form cross-linking gel; putting the gel into a sealed dryer; soaking the gel by ethanol; and drying and screening the gel by a supercritical drying method, so as to prepare the solid absorbent with high CO2 adsorption capacity. The absorbent is low in price, stable in structure, high in carbonic acid conversion ratio, not easy to inactivate, and small in corrosion on equipment, and has certain mechanical strength, and high cyclic utilization rate; and the preparation method of the absorbent is convenient to operate, and low in expenses.