A betaine amphoteric surfactant was synthesized as a selfdirecting agent by oleic acid, 3-dimethylaminopropylamine(PDA) and sodium chloroacetate as the raw materials through a two-step reaction of condensation and quaternization. The effects of catalyst, raw material ratio, reaction temperature, reaction time and other factors on the conversion of oleic acid were investigated, and the optimum process conditions were determined. The synthetic product and the optimum additives form a clean self-diverting acid system which is uniformly stable, has a low viscosity of fresh acid and is easy to pump. When the mass fraction of HCl in the system drops to 3%, the viscosity of the system reaches 219 mPa·s. The acid system breaks when it encounters crude oil. The viscosity of the gel-breaking fluid is 3 mPa·s. There is no residue and it is easy to discharge back. The field application results show that the system has good steering effect and the effect of increasing production after putting into production is obvious.