Method for preparing ecabet sodium

The invention discloses a method for preparing ecabet sodium. The method disclosed by the invention is characterized by comprising the following steps of carrying out sulfonation reaction on dehydroabietic acid (formula III) as a starting material and fuming sulfuric acid to obtain 12-sulfonic dehydroabietic acid (formula II) and enabling the compound shown as the formula II and a sodium-forming agent to form a sodium salt in a solvent system at least containing water to obtain ecabet sodium. By virtue of the method disclosed by the invention, the deficiencies of the prior art are overcome and the method has the advantage of high sulfonation yield and high selectivity in sodium salt forming, simple operation, safety and environment friendliness and is suitable for industrial production.