The Tibetan Plateau has a large area of marshes which play a crucial part in the global carbon cycle. The vegetation aboveground biomass (AGB) is a critical indicator of carbon storage of marsh ecosystems. Due to the limitations of field investigation, the spatiotemporal variation of AGB and its influencing factors of the Tibetan Plateau marshes remain unclear. By using the normalized difference vegetation index (NDVI), climate and measured AGB data, this study investigated the temporal and spatial variation of marsh AGB and its response to climate change in the Tibetan Plateau during 2000-2019. The results showed a good correlation between AGB and annual maximum NDVI (NDVImax), and the AGB can be accurately estimated from a power function equation between marshes biomass and NDVImax (Y = 343.08 x NDVImax0.7363). Based on the function equation, we found that AGB density increased significantly (4.10 gmiddotC/m(2)/decade) from 2000 to 2019 over the Tibetan Plateau, with an average value of 184.71 gmiddotC/m(2). In terms of climate effects, increased precipitation in July could significantly increase marsh AGB, while precipitation in other months has no significant effect on the marsh AGB in the Tibetan Plateau. This study first found an asymmetric impact of night and day temperature on AGB in the Tibetan Plateau marshes: warming day-time temperature has no-significant effect on marsh AGB, while night-time warming can significantly increase the AGB of marshes. Considering the background of global asymmetric warming in nighttime and daytime, more attention should be paid to the different impacts of day and night temperatures on marsh AGB in the Tibetan Plateau.