To analyze the change of optical property of PWS skin during photodynamic therapy, the reflection spectra and fluorescence spectra of PWS skin during PDT treatment were measured using mini-optical fiber spectrograph. The change of reflection spectra and fluorescence spectra were analyzed according to the histological structure of PWS skin and the absorption spectra of the main chromophores in skin (melanin and hemoglobin). The result showed that the spectra changed significantly at the wavelength at which melanin and hemoglobin have high absorption, or at which obvious difference existed in the absorption between HbO2 and Hb. The monitoring of reflection spectra and fluorescence spectra during PDT can provide information about the dynamic change of the optical property of PWS tissue.