Z-scheme heterojunctions can improve the light energy utilization efficiency of TiO2-based semiconductors because of their unique photogenerated carrier transfer pathways. In this study, we used in-situ synthesis strategy to construct a novel π conjugated polymer poly (diphenylbutadiene) (PDPB) doped TiO2 composite system. The as-synthesized 20 wt% PDPB/TiO2 heterojunction shows a Rhodamine B degradation rate of 455.5 mg/h/gc under visible light, which is 272% higher than that of bare TiO2. The structural characterization and test analysis of the photocatalysts reveal the main reasons of the photocatalytic performance enhancement of PDPB/TiO2. The Z-scheme PDPB/TiO2 heterojunctions possesses both the advantages of type II heterojunction and excellent redox ability of PDPB/TiO2 system. Moreover, the introduction of PDPB enhances the visible light absorption range and the specific surface area of the catalyst. This work provides a fresh approach for the involvement of organic polymers in the construction of TiO2-based heterojunction photocatalysts.