The invention discloses a preparation method of a high-temperature-resistant block alumina aerogel, and the method comprises the following steps: dissolving an aluminum source in a mixed solvent of distilled water and ethanol, stirring for 20-50 minutes in a water bath with the temperature of 60-80 DEG C, and cooling to room temperature so as to obtain a mixture solution; adding concentrated nitric acid into the mixture solution under the stirring, adjusting the pH value to 1.6-1.8, then mixing methanol, acetone and a catalyst to obtain a mixture, and then adding the mixture into the mixture solution; and then stirring the mixture for 10-60 seconds, pouring the mixture into a mould to form a gel after 10-30 min, aging the gel, exchanging the solvent with ethanol for three days, and puttingthe wet gel into an ethanol autoclave to carry out supercritical drying to obtain the alumina aerogel. The alumina aerogel is prepared by adopting a sol-gel method to prepare the wet gel and using the supercritical fluid drying method to dry the wet gel, the preparation method simple in process, the reaction process is easy to control, industrial production is easy to realize, and the prepared alumina aerogel is complete in surface, free of cracks, good in high-temperature resistance and wide in application prospect.