Abstract: In order to improve the photocatalytic activity of TiO₂, the poly-2-aminobenzene sulfonic acid modified TiO₂ (P2ABSA/TiO₂) nano particles were synthesized via the in situ oxidative polymerization method. The prepared nano particles were characterized by TEM, EDS, XRD, UV-Vis DRS and Photocurrent Test. The methylene blue was used as simulated pollutants, the synthesis conditions of nano materials were optimized, the influences of initial pH value and P2ABSA/TiO₂ concentration on photocatalytic effect were investigated, the contributions of reactive oxidation species were determined by using trap experiment in photocatalytic process. The results show that the optimum synthesis conditions of P2ABSA/TiO₂ nano particles are P2ABSA, TiO₂ and oxidant amount of substance ratio 2:1:2, HCl concentration 1.2 mol/L. There is a P2ABSA film on the surface of TiO₂. The modification of P2ABSA does not impact on the phase and grain size of TiO₂. P2ABSA/TiO₂ nano particles enhance the response to visible light and photocurrent density (from 18.3 μA/cm² to 28.7 μA/cm²). The photocatalytic degradation rate of methylene blue increases from 92.0% to 99.0%, with initial pH value increasing from 3.93 to 11.36, the optimum concentration of P2ABSA/TiO₂ nano particles is 1.5 g/L. The contribution order of reactive oxidation species in photocatalytic process is ·OH > h⁺ > ·O₂^-, the photosensitization effect of P2ABSA to TiO₂ is a key reason for enhancing photocatalytic activity of P2ABSA/TiO₂ nano particles.