Abstract: Based on systematic investigation and analysis of literature, p aminobenzene sulfonic acid is selected as a typical solute to be separated from dilute solution.An aliphatic,straight chain tertiary amine,7301,is used as complexing agent.Since the pH of aqueous solution is an important factor in chemical complexation extraction of p aminobenzene sulfonic acid,its effect on extraction equilibium is especially studied in the experiments.The effects of concentration of complexing agent and type of diluents on distribution ratio D are also investigated.Meanwhile,the proton transfer equilibrium is discussed.By using Mass Action Law,an expression of equilibrium distribution ratio for 7301 system is proposed.The results show satisfying precision of the model.