The synthetic technology of aminosulfonic acid-based superplasticizer with low residual content of free phenol and formaldehyde was studied in this paper. The results indicate that factors, such as reactants ratio, time, temperature, pH, and so on, influence its dispersing ability and its contents of residual phenol and formaldehyde. The optimized synthetic conditions are as follows: the molar ratio of sodium amino-benzene sulphonate/phenol/formaldehyde is (0.75-1.0): 1: (2.5-5.0); the time is 2.0~3.5h, and temperature is 80~95℃, and the pH of solution is 8.5 ~11.4. The content of residual phenol and formaldehyde in superplasticizer solution produced under the optimized conditions are far below the National Standard of PF resin produ