Abstract: Sulphonated alkylphenol was synthesized with alkylphenol (A) and concentrated sulphuric acid (B), and the effect of reaction conditions on the sulphonation rate was studied. The structure of the prepared sulphonated alkylphenol was characterized by means of FT-IR．Rotary weight-loss method，digital camera，microscope and EDS were used to investigate the corrosion inhibition performance of sulphonated alkylphenol．Results showed that under the optimal reaction conditions of B/A mole ratio of 1.25，a reaction temperature of 60 ℃ and a reaction time of 2 h, the yield of sulphonated alkylphenol could reach 90.46%．Sulphonated alkylphenol used as corrosion inhibitors could suppress the corrosion of A3 steel by naphthenic acid effectively, due to the formation of a protected film on the steel surface. The corrosion inhibition rate reached 93.27% under the following conditions: sulphonated alkylphenol concentration of 1 000 mg/L, corrosive medium temperature of 280 ℃，with a stirring speed of 300 r/min and the residence time in corrosive medium was 6 h．