The invention discloses a soil conditioner and a preparation method thereof and relates to the field of soil conditioners. The soil conditioner is prepared from the following raw materials in parts byweight: 10 to 15 parts of straw particles, 40 to 45 parts of fermented cow dung, 3 to 7 parts of medical stone, 2 to 5 parts of dolomite powder, 5 to 10 parts of modified attapulgite, 2 to 5 parts ofdesulphurization gypsum powder, 4 to 9 parts of seafood shell powder, 5 to 10 parts of plant ash, 4 to 9 parts of sweet potato waste, 4 to 9 parts of fermented residue, 1 to 3 parts of shiitake mushroom extract, 1.5 to 3.5 parts of plant growth agent, 2 to 5 parts of amino acid salt, 1.5 to 3.5 parts of ferric chloride, 3 to 7 parts of ammonium dihydrogen phosphate, 2 to 5 parts of calcium superphosphate and 0.5 to 1.2 parts of microorganism acting bacteria. According to the soil conditioner, the soil fertility can be improved and a soil caking phenomenon is improved; the breathability, seepage, fertilizer-keeping and water retention capabilities of salt-alkali soil are remarkably enhanced; the physical-chemical properties of the soil are effectively improved.