Poplar decline has become increasingly widespread in northern China under intensified warming and drought. However, the sensitivity of radial growth to climatic variability and the drought adaptation mechanisms of declining trees remain limited. In this study, we developed standard tree-ring chronologies for healthy and declining Simon poplar (Populus simonii Carr.) in Jungar Banner on the northeastern Ordos Plateau, northern China. Our objective was to assess their climatic responses and ecological resilience. The results indicated that declining trees chronologies exhibited a higher statistical quality, but showed a long-term decreasing growth trend after 2000, contrasting with the increasing growth trend of healthy trees. The climate-growth relationship of Simon poplar chronologies showed that declining trees are more sensitivity to temperature and water availability. Healthy trees maintained consistently higher resistance, recovery and resilience across drought intensities. In contrast, as drought severity increased, both healthy and declining trees showed declining resistance and resilience, accompanied by enhanced recovery. These findings improve our understanding of the climatic sensitivity and drought-adaptation mechanisms of healthy and declining Simon poplar, and provide valuable insights for enhancing poplar management under ongoing climate change.