Photodynamic therapy (PDT) has been widely used as a precise targeted therapeutic modality in the clinical treatments of malignant tumor and benign diseases. The utilization of advanced optical imaging techniques in the real-time quantification of PDT dosimetric parameters is essential in predicting PDT efficiency and providing personalized and precise treatment. In this study, four important parameters in PDT dosimetry were introduced (i.e., photosensitizer, ground-state oxygen, singlet oxygen, and vascular response). Furthermore, the advanced optical imaging techniques currently developed for monitoring the aforementioned dosimetric parameters are summarized, and the advantages and limitations of each optical imaging technique is comparatively analyzed. Finally, challenges in clinical translation of optical imaging techniques to the clinical application of PDT are briefly discussed.