Robust photosensitizers with strong red/NIR fluorescence, efficient reactive oxygen species (ROS) generation and high photostability are highly desired for photodynamic therapy (PDT). Herein, three novel red conjugated polyelectrolytes (CPEs) with tetraphenylethene and 2,1,3-benzothiadiazole on the main chains and triphenylphosphonium on the side chains are developed. These CPEs display apparent aggregation-induced emission feature and high fluorescence quantum yields in the aggregated state. They can target lysosome in HeLa cells for fluorescence bioimaging. By virtue of the good retention effect and high photostability, these CPEs show ultralong-term tracing performance of subcutaneous tumors, and the tumor site can still be visualized for 20 days after injection. Owing to their good biocompatibility and strong ROS generation ability, the image-guided PDT based on these CPEs can effectively inhibit the growth of subcutaneous tumor and significantly prolong the survival of tumor bearing mice. The H&E and IHC staining reveal that the PDT of these CPEs depress the proliferation of tumor cells, and promote apoptosis and necrosis process. These new CPEs may be employed both as fluorescent probes forin vitroandin vivolong-term tracing and as photosensitizers for image-guided PDT of tumors.