Elevation, as a comprehensive ecological variable, is considered one of the decisive factors in the distribution pattern of plants in a region. We explored changes in functional traits and biomass accumulation and allocation of Gentiana lawrenceni along an elevational gradient and their relationships. We found that leaf size and specific leaf area (SLA) of this species showed a trend of first increasing and then decreasing with elevation, while leaf thickness and leaf dry matter content (LDMC) showed a trend of first decreasing and then increasing. As elevation increases, the aboveground biomass, belowground biomass and total biomass all decline, and above- and belowground biomass allocation is initially reduced and then rise. Leaf size and LDMC positively affected biomass accumulation, while four leaf traits did not affect biomass allocation. In sum, this study found that there is a threshold at ~3600 m above sea level that causes changes in functional traits and biomass allocation strategies of this species to adapt to harsher high-elevation environments. Gentiana lawrenceni can maintain its biomass accumulation and fitness by adjusting leaf size and LDMC. This study has enhanced our understanding of the changes in functional traits, biomass accumulation and allocation strategies of alpine plants along an elevation gradient.