The invention relates to a preparation method of blocky La2O3-Al2O3 composite aerogel. The method comprises the steps that aluminum chlorhydrexusp, hydrated lanthanum inorganic salts, deionized water, absolute ethyl alcohol and propylene oxide are uniformly stirred according to a certain mole ratio, the reaction pH value is regulated with alkali liquid, a colorless and clear La2O3-Al2O3 composite aerogel solution is obtained, and standing is conducted on the colorless and clear La2O3-Al2O3 composite aerogel solution in an environment at certain temperature to wait for gelling; drying treatment is conducted on a sample through a CO2 supercritical drying method to obtain the blocky La2O3-Al2O3 composite aerogel, and the properties such as the heat stability and the pore structure of the blocky La2O3-Al2O3 composite aerogel are inspected by conducting heat treatment on the sample under the aerobic conditions at the high temperature of 1,100 DEG C to 1,300 DEG C. The preparation technology process is simple and easy to operate, and the prepared La2O3-Al2O3 composite aerogel has the advantages of being uniform in nano-pore structure, large in specific surface area, low in heat conductivity and density and the like. The La2O3-Al2O3 composite aerogel which not only has the nano-porous aerogel structure but also has the characteristics of rare earth element oxides can achieve a better application prospect on high-temperature thermal insulation, heavy metal ion adsorption and catalyst and catalyst carriers.