Abstract: The photosynthesis and its response of Kobresia humilis, which were obtained from different altitudes in Qinghai Plateau, to the glowing environmental conditions and cold stress were studied. The results showed that the chlorophyll content in the K. humilis leaves tended to decrease with increasing altitude, but the chlorophyll a to b ratio and the carotenoid content increased. The photosynthetic rate, light compensation point and light saturation point increased with the increase of altitude, and the photorespiration rate declined. The photosynthetic apparent quantum yield of K. humilis grown in the culture room (PAR: 60—70 μmol·m-2·s-1 mean day/night temperature: 15℃/10℃) was higher than that grown in the green house (PAR. highest 1250 μmol·m-2·s-1; mean day/night temperature: 24℃/13℃), whereas the photosynthetic rate and Hill Reaction rate were the opposite. The optimum photosynthetic temperature varied with the growing temperatures and the original growing altitudes. The photosynthetic rate and apparent quantum yield of K. humilis decreased after being subjected to cold stress. The cold stress was more inhibitive to the photosynthetic rate under light (90—100 μmol·m-2· s-1) than under dark conditions.