Nano-sized TiO2 prepared by a sol-gel method was used as photoelectrocatalyst and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Brunaue-Emmett-Teller (BET). Electric field assisted photocatalytic properties of TiO2 were characterized by the degradation of methylene blue. Results show that TiO2 possesses small particle size and high effective degradation rate on the degradation of methylene blue. But the photo-degradation performance of TiO2 decreases with the synergy of electric field. It should be resulted from the loss of photocarrier that are neutralized with the positive and negative charge of the electric field before forming over oxidation groups. It could be deduced that the electric field inhibits the photocatalytic performance of TiO2 catalyst. It is also found that the degradation of methylene blue are in accordance with the Langmuir-Chinshelwood function mode.