<p>Seedling regeneration is a key process for ecological recovery and the foundation for maintaining forest stability and sustainability. However, our understanding of how biotic and abiotic factors influence seedling survival is still incomplete, especially in Qinghai spruce forests that are highly sensitive to climate change. In this study, we compiled three years of data on 12,432 seedlings in Qinghai spruce forests on the northern Qinghai-Tibet Plateau to evaluate how biotic interactions—primarily conspecific density dependence—and spatially variable abiotic conditions jointly influence seedling regeneration across different height classes. Our results show that seedling survival was primarily driven by initial seedling height and environmental variation, while responses to density dependence were comparatively weak. Canopy structural variables, such as canopy gap fraction and mean leaf inclination angle (MLA), emerged as key predictors of regeneration success, reflecting the influence of forest structure on the potential light environment. The influence of environmental factors on density dependence varied in both strength and direction: Conspecific density dependence shifted from negative to positive with increasing canopy openness and slope but reversed from positive to negative with improved soil quality. Furthermore, as seedling height increased, the relative importance of initial seedling height for survival diminished, while environmental factors and biotic interactions became more prominent. Overall, our study highlights that seedling height and forest structural heterogeneity are the most significant factors driving seedling regeneration in Qinghai spruce forests, with environmental factors and biotic interactions playing increasingly important roles as seedlings grow. These findings provide valuable insights into the mechanisms underlying seedling survival and inform the conservation and management of spruce forests.</p>