NOVELTY - A guaiacol sulfonic acid potassium is prepared by using 50-98 mass% sulfuric acid as solvent and sulfonating agent, reducing sulfuric acid to temperature to - 5-10 degrees C, adding phthalic dimethyl ether, stirring under heating to 30-80 degrees C, reacting for 3-8 hours, controlling pH to 7-9 by adding calcium oxide or calcium carbonate, filtering reaction liquid, adding Lewis acid, heating to 60-100 degrees C, reacting for 2-5 hours, controlling temperature to 20-30 degrees C, adding potassium carbonate, potassium bicarbonate, or potassium hydroxide, heating, reacting, and filtering to remove insoluble substance.    USE - Preparation of guaiacol sulfonic acid potassium (claimed).    ADVANTAGE - Preparation process is environment-friendly and low-cost and has mild reaction condition.    DETAILED DESCRIPTION - A guaiacol sulfonic acid potassium is prepared by using 50-98 mass% sulfuric acid as solvent and sulfonating agent, reducing sulfuric acid to temperature to - 5-10 degrees C, adding phthalic dimethyl ether, stirring under heating to 30-80 degrees C, reacting for 3-8 hours, controlling pH to 7-9 by adding calcium oxide or calcium carbonate, filtering reaction liquid to obtain 3,4-dimethoxy-benzenesulfonic acid calcium, adding Lewis acid, heating to 60-100 degrees C, reacting for 2-5 hours, controlling temperature to 20-30 degrees C to obtain 3-hydroxy-4-methoxy-benzene sulfonic acid calcium 4-hydroxy-3-methoxy-benzenesulfonic acid calcium, adding potassium carbonate, potassium bicarbonate, or potassium hydroxide, heating to 50-100 degrees C, reacting for 2-10 hours, controlling temperature to - 10-0 degrees C, and filtering to remove insoluble substance in which mole ratio of sulfuric acid and phthalic dimethyl ether is 1-3:1, mole ratio of 3,4-dimethoxy-benzenesulfonic acid calcium and Lewis acid is 1-1.1:1, and mole ratio of 3-hydroxy-4-methoxy-benzene sulfonic acid calcium 4-hydroxy-3-methoxy-benzenesulfonic acid calcium and potassium carbonate, potassium bicarbonate, or potassium hydroxide is 1:1-1.1.