This paper revealed a mechanism of sulfomethylation of condensing and sulfomethylating of biphenol A,which is analyzed by UV-spectra,IR-spectra and viscosity,and solubility.The results showed that the sulfomethylation of biphenol A could be divided into three steps.Before 1.5h concerne the cndensation of biphenol A resulting in the increment of viscosity,At 2.0h the synthesize proceed the sulfomethylation by test of IR and S contained in the product.After 2.5h was the condensation and sulfomethylation simultaneously.The solubility in acidic water and viscosity of the products increase with the time go.The element analysis shows that the propotion of C∶H∶S∶O was 35∶40∶2∶2∶11,The final products are dimmer or quartmer.