Pinus densata is an endemic and dominant conifer in subalpine forests along the southeastern margin of the Tibetan Plateau, where it plays important ecological roles and provides high-resolution tree-ring records for assessing climate–growth relationships. However, the extent to which climatic controls on growth vary among sites with contrasting habitat conditions within the same region remains insufficiently resolved. In this study, we investigated P. densata at three sites in northwestern Yunnan, southwestern China: Yulong Snow Mountain (YL), Haba Snow Mountain (HB), and Shika Snow Mountain (SK). Residual tree-ring width chronologies were developed and analyzed by using response function analysis, redundancy analysis (RDA), and moving-window correlation analysis to identify key climatic factors and evaluate site-specific and temporal variation in growth–climate relationships. The results showed that radial growth responses differed markedly among sites. At YL and HB, ring width was negatively associated with mean temperature in May and positively associated with May precipitation, suggesting that early-growing-season moisture availability may play an important role under warm conditions before full monsoon onset. Warmer conditions in August generally favored growth at both sites. In contrast, radial growth at SK was positively associated with September mean temperature, suggesting a stronger association with late-growing-season thermal conditions at the higher-elevation site. RDA further retained current May mean temperature, current August mean temperature, and previous December precipitation as significant explanatory variables, indicating that radial-growth variation was linked to both current-year thermal conditions and antecedent winter moisture. Moving-window analysis showed that growth–climate relationships varied in strength and direction over time, with distinct site-specific patterns. Overall, these findings indicate that climatic responses of P. densata radial growth in northwestern Yunnan showed spatial heterogeneity and temporal non-stability. This study provides dendroecological evidence that site-level differences and temporal non-stability should be considered when assessing the potential responses of monsoon-influenced subalpine forests to ongoing regional warming.