A simulation experiment of short-term supplementation of UV-B was conducted to study the changes of chlorophyll fluorescence coefficients of alpine plant Saussurea superba under three typical weather conditions (sunny, cloudy, and shady) in Qinghai-Tibet Plateau. When the weather changed from sunny to shady, the maximal quantum efficiency of PS II photochemistry (F(v)/F(m)) after 3 minutes of dark adaptation increased significantly, the actual photochemical efficiency of PS II (phi(PS II)) and photochemical quenching (q(P)) also increased, but the non-photochemical quenching (NPQ) decreased, demonstrating that PAR was the main factor affecting the PS II photochemical efficiency of S. superba. After the short-term supplementation of UV-B, the F(v)/F(m) and NPQ under the three typical weather conditions had a slight decrease but the phi(PS II) and q(P) had a slight increase, while the photosynthetic gas exchange had less change. The increasing trend of net photosynthetic rate P(n) and psi(PS II) under enhanced UV-B radiation could be related to the existence of more UV-A component, and also, benefited from the increased leaf thickness. UV-B radiation had potential negative effects on leaf photosynthetic components.