The invention discloses a method of improving the sulfonation reaction efficiency. Sulfonation is promoted by removing water generated in a sulfonation reaction. The method is characterized by comprising the step: in a sulfonation reaction process, keeping constant pressure or vacuum, and introducing gas into a reaction system, wherein water in the reaction system is taken away as gas flows out. The invention also discloses a production method of a dispersant MF. With adoption of the sulfonation method, the dispersant MF product is obtained by means of condensation and neutral reactions. In the whole process, unmanageable solid wastes are not generated, the content of sodium sulfate of the obtained product is lower than 5%, and the product can resist 150 DEG C and meets the first grade standard.