The invention relates to a preparation method of a neutron absorption composite material with the high neutron absorption rate. The preparation method comprises the following steps that 1, by weight, 8-40 parts of boron carbide powder, 32-96 parts of aluminum alloy powder and 0.1-10 parts of light rare earth powder are weighed; 2, the boron carbide powder, the aluminum alloy powder and the light rare earth powder are added into powder mixing equipment to be mixed; 3, the materials which are mixed by the power mixing equipment to be uniform are added into a vacuum sintering furnace to be sintered, and a rolled compact is obtained; 4, an aluminum alloy layer with the thickness of 0.05-1 cm is poured to the four side walls of the rolled compact; and 5, 3-8 passes of hot rolling treatment are carried out after mold pressing, 450-500 DEG C annealing treatment is carried out between rolling passes, and therefore the neutron absorption composite material with the high neutron absorption rate is obtained. The metallurgical quality of the material is ensured, and it is ensured that the composite material has the excellent mechanical property, heat conductivity and neutron absorption capacity.