The effects of ultraviolet-B (UV-B) radiation on protein structure in photosystem Ⅱ (PSⅡ) was studied using Fourier transform infrared spectroscopy. The results demonstrated that irradiation of the plant with enhanced UV-B caused the change in the structures of protein in PSII. The intensity of α-helix, β-sheet was increased, while the intensity of β-turn was decreased. The coupling of those structures with surrounding became weaker with UV-B radiation. Otherwise, the UV-B influenced the structure of tyrosine residue and made the polarity of tyrosine decrease. The changes caused by UV-B radiation could alter the combination between Mn cluster and pigments with protein inevitably. It would lead to a series of changes, such as the process of light transmission and conversion, electron transfer and oxygen evolution.