How and why biodiversity varies along the elevational gradients is fundamental yet controversial topics in ecology. To advance our understanding on these questions and provide insight into biological conservation, we explore the elevational patterns of vascular plant richness and their drivers in the Gyirong Valley, the longest valley in China’s Himalayas. Elevational richness patterns of vascular plant were documented by 96 sampling plots along 12 elevational bands of 300-m ranging from 1800 to 5400 m above sea level. We related the elevational patterns of vascular plant richness to the climate, spatial, historical, and disturbance factors, and assessed the relative importance of these factors in explaining above patterns using the Random Forest model. Overall, the species richness of vascular plant showed a hump-shaped pattern along the elevational gradient in the Gyirong Valley, although the life form and endemism of species in combination with the scale effect modified the patterns observed. Climate factors played a greater role than other environmental factors in explaining the elevational pattern of vascular plant richness. Such strong climate-species relationship was nicely interpreted by the water-energy dynamic hypothesis, indicating the combined effect of energy and water is the major driver that shaped vascular plant richness along elevational gradient. The climate-driven hump-shaped pattern of vascular plant in the Gyirong Valley is aligned with most of previous report from different part of the Himalayas, highlighting the need for more conservation effort at the intermediate elevations of this region, and calling for more scientific concern on the impact of climate change on elevational pattern of biodiversity.