The elevational divergence of plant CSR (Competitor–Stress-Tolerator–Ruderal) strategies represents a core theme in global change ecology, yet adaptive patterns across subalpine transition zones remain insufficiently understood. This study focused on 375 plant individuals sampled along an 1143–4361 m elevational gradient on Gongga Mountain. We divided elevations into three zones (low, mid, high) using tertile partitioning, measured leaf functional traits including leaf area (LA), specific leaf area (SLA), and leaf dry matter content (LDMC), and quantified CSR strategy scores with the StrateFy approach. We further explored how hydrothermal factors drive community- and intraspecific-level strategy variation. Results showed that CSR strategies differed significantly along the elevational gradient. The relative abundance of individuals with the C strategy was 53.4% at low elevations, peaked at 72.4% at mid elevations, and decreased to 43.6% at high elevations. By contrast, the S strategy was most abundant at high elevations (32.5%), while the R strategy consistently accounted for less than 5% across all zones. Life form-specific strategies varied strongly: herbs maintained a dominant C strategy (66.7%) at high elevations; trees shifted to S strategy dominance (60%) at high elevations; and shrubs displayed a balanced C–S strategy. Intraspecific plasticity in CSR strategies was pronounced: with increasing elevation, the dominant strategy shifted from C (33.3%) to S (66.7%), with a greater magnitude of variation than at the community level. Temperature was positively correlated with the C strategy (p < 0.001, R² = 0.53) and negatively correlated with the R strategy (p < 0.001, R² = 0.40). Precipitation was negatively correlated with the C strategy (p = 0.001, R² = 0.54) and positively correlated with the R strategy (p = 0.005, R² = 0.42), whereas both factors exerted weak effects on the S strategy. Our findings highlight that shifts in hydrothermal conditions are the primary drivers shaping CSR strategy distributions, and coordinated leaf trait variation serves as a key adaptation mechanism. These results improve mechanistic understanding of mountain plant adaptation and provide a scientific basis for alpine vegetation conservation and management.