The Qinghai-Tibet Plateau is a sensitive region to global climate change, which has a large area of marshes wetland. As a core component of marsh ecosystems, marshes vegetation plays an important role in land surface energy exchange, biogeochemical cycle and hydrological cycle in the Qinghai-Tibet Plateau. Understanding the spatio-temporal change of marshes vegetation and its response to climate change can stimulate insights on the relationship between marshes vegetation and climate change, and provide evidence to guide wetland vegetation conservation and restoration in the Qinghai-Tibet Plateau. Based on the Normalized Difference Vegetation Index (NDVI) data, monthly precipitation, mean temperature, maximum temperature, and minimum temperature data, this study analyzed the spatio-temporal change of marshes NDVI and its response to climate change in the Qinghai-Tibet Plateau during the growing season from 2000 to 2017. The results showed that the long-term averaged growing season NDVI of marshes increased from northwest to southeast in the Qinghai-Tibet Plateau; the mean growing season NDVI of marshes showed an overall increasing trend (0.010/10a) from 2000 to 2017. The area where the mean growing season NDVI increased accounted for 78.25% of the entire study area. There was a weak correlation between the marshes NDVI and precipitation, indicating that precipitation may not be the main factor affecting the growth of marshes vegetation in the Qinghai-Tibet Plateau. There was a significant positive correlation between the growing season NDVI and mean temperature, maximum temperature and minimum temperature, which indicated that the growth of marshes vegetation was mainly affected by temperature in the Qinghai-Tibet Plateau, and the increase of temperature could obviously promote the growth of marshes vegetation. In addition, we found for the first time that the daytime and night-time warming had an asymmetric effect on the marshes vegetation in the Qinghai-Tibet Plateau. The correlation between the growing season NDVI and the minimum temperature was higher than the correlation between the growing season NDVI and the maximum temperature, indicating that the effect of night-time warming on the growth of marshes vegetation was more obvious in the Qinghai-Tibet Plateau. Under the background of global daytime and night-time asymmetric warming, more attention should be paid to the asymmetric effects of day and night temperature on the marshes vegetation in the Qinghai-Tibet Plateau, especially when we want to use the model to simulate the impact of future climate change on the marshes vegetation in this area.