Abstract: Through the systematical measurements of δ¹³C values of samples representing 25 families and 86 C3 herb species along the slope aspects in an alpine meadow, the responses of δ¹³C va-lues and water use efficiency (WUE) for C3 plants to slope aspect changes and influence of environmental factors were analyzed and main environmental factors related to plant δ¹³C values change were revealed. Along the north-facing to south-facing slope, soil water content decreased gradually, the soil temperature and light intensity increased gradually, and plant community structure also had corresponding change. The δ¹³C values of C3 plant species in 5 slope aspects were from -31.19‰ to -21.8‰, with an average value of (-27.18±0.13)‰. The average δ¹³C value was the highest along the south-facing slope, followed by that along the southwest slope, west slope and northwest slope, with the lowest along the north slope during the whole growing season. The difference of δ¹³C values among the different slope aspects were caused by discrepancy in soil water content, soil temperature and light intensity. Soil water content was the main limiting factor. From north slope to south slope, plant δ¹³C value increased with the increasing soil temperature, light intensity and the reducing soil water content, which suggested that different species had different strategies to adapt to environmental changes of drought stress in different slope aspects, and water use efficiency was improved gradually in order to adapt to the environment of drought stress.