The invention relates to a preparation method of 3, 3-diaminodiphenylsulfone, which comprises adding iron powder with solvent in weak acid property, to reduce 3, 3-dinitrodiphenylsulfone into 3, 3-diaminodiphenylsulfone. The inventive method is beneficial for reaction and the reaction is complete, the invention processes purification after the reaction to obtain high-purity white crystal, the mother liquor is deposited, depressurized and distilled to recover solvent for reuse. In the reaction, sulfolane solvent can be added into the reaction to shorten the reaction time to 2-6h, thereby improving reaction selectivity, and sulfolane can be circulated in the preparation while the loss is 5%, to improve solvent utilization and reduce cost.