The invention discloses a self-heat preservation building block produced by using industrial byproduct gypsum and a preparation method thereof. The preparation method comprises the following steps of: preparing 43-46 parts by weight of industrial byproduct gypsum, 14-16 parts by weight of steel slag, 4-6 parts by weight of kaolin, 0.30-0.40 parts by weight of micro mineral powder, 18-22 parts by weight of cement and 4-6 parts by weight of volcanic ash excitant, finely grinding into to 200 meshes through a Raymond mill, then adding 4.0-5.0 parts by weight of hydrogen peroxide, 3-6 parts by weight of hydroxypropyl methyl cellulose, 2-4 parts by weight of heat stabilizer and 35-45 parts by weight of 40-45 DEG C warm water, stirring and mixing, pouring into a mold, carrying out wet maintenance for 3-4 hours after molding, and carrying out normal temperature maintenance for 10-15 days. The preparation method has the advantages that a conventional method for producing light-weight thermal mortar by taking cement as a main raw material and adding materials such as pulverized fuel ash and slag is broken through, gypsum serves as a bran-new binding material to be applied to the mortar, a production technology is simplified due to adoption of a calcination-free technology, and the shortcomings of high investment, high cost, energy dissipation and pollution existing in a conventional calcination technology are overcome.