Because of the enhanced of solar UVR and the destruction of Sargassum horneri in Nanji archipelago, it is necessary to study the effect of solar UVR on growth and photophysiology of S. horneri, in order to recovery algae forest by artificial seeding. We carried out experiments using long-term exposure with three radiation treatments, photosynthetically active radiation (PAR, 400-700 nm); photosynthetically active radiation + Ultraviolet A (PA, 320-700 nm) and photosynthctically active radiation+Ultraviolet A+Ultraviolet B (PAB, 280-700 nm) respectively. Big quartz tubes with thalli, which were put into 10℃ thermostatic baths with running tap water, were exposed to three different solar radiations for 14 days acclimation. At the end of experiment, the relative growth rate (RGR) of S. horneri was promoted by 6.7% in UV-A (PA treatment), while was inhibited by 8.98% in UV-B (PAB treatment) compared with P treatment. The results of photosynthetic pigments and chlorophyll fluorescence characteristics revealed that the UV-A significantly raised the concentrations of chlorophyll a, carotenoid and UV-absorbing compounds (UVACs), but UV-B do decrease the pigments. Moreover, UV-A had a significantly positive effects on the maximum relative electron transport rates (rETR_max) and the light utilized efficiency (α). After 14 days acclimated under solar radiation, the thalli were removed indoor to re-exposed to the artificial solar lamp (PAR=213.3WUV-A=14.3WUV-B=6.7 W) in order to check the short-term response to elevated UVR. The results shown the repair rate (r) of D1 protein is faster in UV-A than in both PAR and UV-B significantly. But the damage rate (k) has not difference among three radiation treatments.