Abstract: The pigment content, chlorophyll fluorescence parameters and photosynthetic electron transport activities of thylakoid membranes were investigated in Polygonum viviparum grown at three different altitudes on the Tianshan Mountains. As altitude increased, the values of Chl (a+b) and Chl b decreased, while the values of Chl a/b, Car/Chl and NPQ increased. F_v/F_m was slightly higher in the leaves at 3 400 m than that at 2 200 m though the difference was not significant, whereas at 3 900 m, it had the lowest values and was significant (P<0.05). F_v/F₀ was stable in leaves at 2 200 and 3 400 m, but at 3 900 m, it became smaller (P<0.05). From 2 200 to 3 900 m, F₇₃₄/F₆₈₆ decreased significantly (P<0.05). The activities of PSⅠ, PSⅡ and the whole chain electron transport activity decreased with an increase in altitude. The decrease in the whole chain of photosynthetic electron transport activity was mainly attributable to the decrease in photosynthetic electron transport activity of PSⅠ, especially at 3 900 m. The study revealed that PSⅠ suffered more servere photoinhibition than PSⅡ at higher altitudes, and the decrease in whole chain electron transport activity of leaves exposed to low temperature and strong irradiation was caused mainly by PSⅠ photoinhibition.