A method for producing potassium sulfate from magnesium sulfate-metachloride potassium-containing brine comprises the following steps: 1, injecting the magnesium sulfate-metachloride potassium-containing brine into a sodium chloride saltern, and naturally spreading sodium chloride saltern to precipitate primary carnallite ore and secondary carnallite ore; 2, mixing and decomposing the primary carnallite, water or brackish water and a conversion mother liquor, and carrying out conversion, floatation and separation to obtain picromerite concentrate and the conversion mother liquor; 3, mixing the secondary carnallite ore, water or brackish water and the above obtained potassium mixed secondary conversion mother liquor, and carrying out decomposition, separation and washing to obtain crude potassium chloride; and 4, mixing and converting the crude potassium chloride, the picromerite and the water or brackish water. The method has the advantages of no external addition of sulfate ions, no introduction of a floatation agent in the production process of the crude potassium chloride, removal of ore milling and floatation processes, convenience in operation, easiness in control, high raw material utilization rate, no pollution, and reduction of the factory building investment by 10-20%.