Long chain polyethylene glycol (Polyethylene Glycol, PEG) is connected with Pyro and small molecule folic acid to develop a novel photodynamic therapy drug. The Pyro is a potential photosensitive compound, and has high singlet oxygen production capacity and high extinction coefficient. Folic acid molecules have strong affinity to tumor cells. The novel long chain polyethylene glycol-modified folic acid targeting Pyro photosensitizer can significantly increase the accumulation ability of the photosensitizer in tumor tissues, and significantly improves the photodynamic therapy effect of the photosensitizer, and the polyethylene glycol with different chain lengths have different influence on enrichment of the photosensitizer in a tumor site and the photodynamic therapy effect of the photosensitizer.