Abstract: Polyvinyl chloride (PVC) was heat-treated in a vacuum at 270℃ to prepare a partly conjugated derivative (CDPVC) through a reaction of remove HCl. The nano TiO₂/CDPVC composite was prepared by compounding commercial TiO₂ and CDPVC with the mass ratio of 2:1 in a high-energy ball-miller, and was characterized by TEM, XRD, XPS, FTIR, SEM and Raman, et al. The photocatalytic degradation of rhodamine B (Rh B) and the photocatalytic reduction of K₂Cr₂O₇ were used to evaluate the visible photocatalytic activity and stability of the nano TiO₂/CDPVC composite. The results show that the structure of Ti-O-C formed by compounding TiO₂ and CDPVC in a high-energy ball-miller, which is advantageous to the improvement in both visible-light absorption capacity of the nano TiO₂/CDPVC composite and separation efficiency of photogenerated electron/hole pairs. Compared to nano TiO₂ and TiO₂-CDPVC (an ordinary product after grinding TiO₂ and CDPVC), nano TiO₂/CDPVC composite exhibits the higher visible-light photocatalytic activity and excellent stability. The visible-light photocatalytic mechanism can be proposed that CDPVC adsorbs photos to produce photogenerated electron-hole pairs, and the photogenerated electrons can be easily injected into the conduction band of TiO₂. The photogenerated electrons (e_CB^-) in CDPVC and conduction band of TiO₂ can be captured by oxygen on the surface of the TiO₂/CDPVC composite to form·O_-² radicals, and·O_-² radicals can directly degrade rhodamine B molecules even to produce H₂O and CO₂.