Method of manufacturing potassium sulfate

This improved method comprises a first dry step of reacting concentrated sulfuric acid and potassium sulfate with potassium chloride at about 300 DEG C. in a slurried state to obtain a mixed slurried salts of KnH2-nSO4 (n being 1.3 to 1.4); a second wet step of dissolving said mixed salts and additional raw potassium chloride in water, the amount of water being limited to some extent, heating the solution to 60 DEG to 90 DEG C. in order to take place a wet reaction, and cooling the solution to 50 DEG to 20 DEG C. to deposit potassium sulfate crystals from the solution in order to obtain the final product and filtrate; and a third circulating step of evaporating the filtrate to obtain a cake of mixed salts of acid potassium sulfate and potassium chloride, and returning circulatingly the cake to the first stage as part of raw materials.