Abstract: Increase in UV-B radiation on earth resulted from continual destruction of atmosphere ozone layer can have significant effects on growth of plants. The effects of enhanced different intensities of UV-B radiation on diurnal variation of photosynthesis on the leaves of Cabernet Sauvignon were studied under natural sunlight condition in order to provide more bases. The results showed that under the treatments of UV-B radiation, there were double peak in the diurnal variations of photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration rate, and the sequence was: Lower radiation treatment(T1, 10.8 μW/cm²) >CK>Higher radiation treatment(T₂, 25.6 μW/cm²), and the sequence of water use efficiency was CK>T1>T2. But the content of photosynthetic pigments was not obviously influenced compared with that of CK. Such results indicate that the effects of enhanced UV-B radiation on photosynthesis in grapevine are related to different intensities of UV-B radiation and treatment time, and that reasonable enhanced UV-B radiation does not do harm to photosynthesis in grapevine.