The transition toward a sustainable built environment necessitates a paradigm shift from mitigating environmental impact to actively regenerating ecological systems. This paper proposes a three-dimensional symbiotic framework for green space planning in high-density urban contexts, integrating design for people, people-nature coexistence, and nature itself. Grounded in the principles of biophilic design and ecological restoration, the framework moves beyond conventional sustainability by emphasizing multi-scalar green infrastructure, biodiversity-sensitive construction, and community-inclusive spaces. Its practical application is examined through in-depth case studies from Hong Kong, including the Zero Carbon Building’s urban native forest, the Jordan Valley Nullah ecological revitalization, and the Kai Tak development’s multi-layered green spaces. These examples demonstrate how the systematic incorporation of native planting, wildlife-integrative architecture, and vertical greening strategies can significantly enhance urban biodiversity, improve microclimatic conditions, and promote mental and physical well-being. The study further highlights the importance of cross-sector collaboration among planners, architects, policymakers, and local communities in implementing such regenerative models. Supported by ecological governance and lifecycle-based design standards, the framework provides a replicable model for high-density cities seeking to align urban development with ecological and social resilience. It is concluded that this integrative approach offers a viable pathway for the post-2030 urban agenda, positioning cities not merely as human habitats but as thriving, biodiverse ecosystems.