Photodynamic therapy (PDT) has shown significant advantages in tumor treatment due to its minimally invasive nature, low toxicity, and high selectivity. This article systematically reviews the research progress of organic photosensitizers (PSs) used in tumor PDT in recent years, and classifies them into six major categories based on chemical structure: porphyrins, chlorins, phthalocyanines, fused quinones, phenothiazines, and BODIPYs. It focuses on the innovative applications of various PSs in molecular design optimization, regulation of photophysical properties, nanonization strategies, and multimodal synergistic therapy. Strategies such as targeted delivery, microenvironment modulation (e.g., hypoxia alleviation, GSH depletion, pH responsiveness), and Type I photodynamic mechanisms have significantly enhanced PDT efficacy. Combined with two-photon excitation, NIR-II window absorption, and imaging guidance, the tissue penetration and treatment precision of PSs have been improved, providing a systematic reference for the development of efficient and low-toxicity tumor PDT strategies.