Against the backdrop of China’s urbanization and the declining trend in residents’ happiness, this chapter examines the complex relationship between the built environment and life satisfaction in high-density urban contexts. Focusing on the central urban area of Guangzhou, it aims to elucidate both the direct and indirect pathways through which objective built environment factors influence residents’ overall cognitive evaluation of subjective well-being. Drawing on questionnaire survey data and statistical modeling, the study integrates a conceptual framework incorporating four key mediators: Perceived Environmental Quality (PEQ), Perceived Safety (PES), Social Capital (SC), and Self-Rated Health (SRH). Section 10.1 presents comprehensive research conclusions, detailing the direct effects of built environment factors such as Building Density, Functional Mix Diversity, and transportation infrastructure on life satisfaction, and further unveils complex mediation mechanisms through structural equation modeling. Section 10.2 discusses research implications and policy recommendations tailored for high-density urban areas, proposing a holistic policy framework that addresses density management, transit optimization, and mediating factor enhancement. Section 10.3 critically reflects on research limitations—including geographic specificity and methodological constraints—and suggests future directions for multi-scale and multi-context built environment analysis. This chapter contributes to the adaptation of compact city theory and environmental psychology within high-density Chinese urban settings, offering evidence-based insights for planning and policy interventions aimed at enhancing residents’ quality of life.