The invention discloses a method for preparing magnesium oxide aerogel with bischofite as a material. The preparation method comprises the following steps: (1) bischofite, distilled water, alcohol solvent and water-soluble polymer are mixed and stirred for 5 to 120 minutes, so that a transparent solution is obtained, and an epoxy compound is then added into the solution and stirred for 5 to 60 minutes, so that a sol is obtained; (2) the prepared sol is sealed for gelation, the temperature of gelation is 20 DEG C to 95 DEG C, the time of gelation is 2 to 20 hours, and thereby a wet magnesium oxide gel is obtained; (3) the obtained wet magnesium oxide gel is immersed and washed with distilled water for not less than three times, and the usage of the distilled water is not less than the volume of the wet magnesium oxide gel; (4) after immersion and washing in step 3, the magnesium oxide gel is dried, and thereby the magnesium oxide aerogel is prepared. The method effectively solves the problem that magnesium alkoxide is extremely easy to hydrolytically polycondense and the process is not easy to control in the conventional preparation of wet magnesium oxide gel by utilizing the magnesium alkoxide and the problem that the magnesium alkoxide is highly toxic, expensive and extremely sensitive to the temperature and humidity of the environment, and is not easy to synthesize and store.