The invention belongs to the field of building materials utilizing the method of preparing gas concrete clayey sandstone which is characterized in that the method comprises the following steps: 1) preparing raw materials; and 2) choosing raw materials: (1) choosing dry materials: the dry materials include the following components by the weight percentages: 52% to 65% of clayey sandstone powder; 12% to 18% of cement; 21% to 30% of quicklime; 2% to 3% of gypse; aluminum powder which takes the 0.085% to 0.12% of the total mass of the clayey sandstone powder, the cement, the quicklime and the gypse; and admixture which takes 0.06% to 0.09% of the total mass of the clayey sandstone powder, the cement, the quicklime and the gypse; (2) choosing water by the mass ratio of water to the dry materials being 0.55 to 0.65; 3) firstly, evenly mixing the clayey sandstone powder, the cement, the quicklime, the gypse and the admixture, then adding the water and stirring evenly; then adding the aluminum powder and stirring for 60 seconds at the temperature of 42 to 47 DEG C to obtain slurry; 4) casting, curing and standing to blow off steam; and 5) after cutting, removing the mould and curing to obtain the gas concrete. The solid waste clayey sandstone obtained by the method has the advantages of high utilization rate and environment friendliness.