As important supplementary green spaces in high-density urban environments, sky gardens have been increasingly recognized for their potential to promote public physical and mental health. Existing studies have preliminarily evidenced their restorative benefits; however, the underlying mechanisms linking spatial environmental characteristics, physiological responses, and psychological perceptions remain insufficiently understood. In particular, there is still a lack of evidence-based guidance at the level of specific spatial elements, which limits the translation of theoretical findings into practical design and optimization strategies. Against this background, this study takes sky gardens as a research object and aims to systematically measure, interpret, and optimize their restorative benefits from an integrated "spatial-physiological-psychological" perspective. First, drawing on computer vision-based semantic segmentation and a comprehensive literature review, key spatial composition elements and restorative indicators of sky gardens are identified, providing a quantitative foundation for subsequent analysis. Based on this framework, eye-tracking experiments are conducted to capture individuals' visual physiological responses during restorative processes, including attention allocation and visual stress indicators. Meanwhile, psychological restorative perceptions are assessed using the perceived restorativeness scale, covering dimensions such as being away, fascination, coherence, and compatibility. By integrating objective physiological data and subjective psychological evaluations, this study constructs a hierarchical association model linking spatial attributes, visual physiological responses, and psychological restorative outcomes. Subsequently, the proposed "spatia-physiological-psychological" model is applied to different types of sky gardens to identify key spatial indicators that significantly influence restorative benefits. To further enhance the applicability of the findings, an importance-performance analysis (IPA) is employed to distinguish priority spatial elements that require targeted intervention and optimization in design practice. This approach allows not only the identification of influential factors, but also the formulation of practical strategies for improving restorative performance under constrained urban conditions. The results reveal several notable patterns. First, spatial scale and visual depth are identified as critical factors in alleviating visual physiological stress, indicating that appropriate spatial openness and depth perception play a vital role in reducing visual load. Second, sky gardens designed at an embodied scale significantly enhance psychological restorative experiences, particularly in terms of temporarily forgetting responsibilities and obligations, alleviating fear and tension, and fostering immersive engagement with the environment. Third, users generally demonstrate a high level of acceptance of sky gardens within high-density urban living contexts. Among spatial attributes, void-to-solid ratio, sky openness, and facility cleanliness exhibit consistently positive effects on restorative benefits. In contrast, the effects of green landscapes are found to be dual in nature, showing both positive and negative influences depending on their spatial configuration and quality. This finding highlights the necessity of flexibly selecting appropriate indicators to represent greenery quality rather than relying solely on quantity-based measures. Overall, this study provides an integrated analytical framework for understanding and optimizing the restorative benefits of sky gardens by bridging spatial design, physiological responses, and psychological perceptions. By combining computer vision techniques, eye-tracking data, and subjective evaluations, the research offers evidence-based insights that support more precise spatial control and targeted design interventions. The findings contribute not only to the theoretical understanding of restorative environments in high-density cities, but also to the practical guidance for designing and upgrading sky gardens to better support public health and well-being.