Abstract. Net primary production (NPP) is a fundamental property of natural ecosystems. Temporal variation of NPP not only reflects how communities respond to environmental fluctuations, but it also has important implications for regional carbon assessment. Unfortunately, studies based on field measurements to directly address this issue in the extreme environment of alpine grasslands are rare. In this study, we measured aboveground NPP (ANPP) and species richness in 40 sites across the Tibetan alpine grasslands from 2006 to 2009 to investigate the regional pattern of temporal variation in ANPP and to quantify the effects of climate fluctuation and biodiversity on this variation. The results showed that, during the four-year period, the average ANPP varied 1.5-fold, from 83.9 to 125.7 g m–2, with a mean coefficient of variation of temporal variation of 36.6% across the 40 sites. Due to the regionally similar climatic fluctuations caused by South Asian monsoons, aboveground NPP exhibited synchronous temporal variation and consistent spatial patterns over the four-year period. Moreover, rainfall fluctuation had a more profound effect on the ANPP dynamics than temperature variation, which suggests that production in the Tibetan alpine grasslands is primarily driven by precipitation. Therefore, the Tibetan alpine grasslands are mainly constrained by water availability. Finally, we found that species richness negatively correlates with variation in aboveground NPP, which might provide evidence that diversity can stabilize community production in high-altitude grasslands.