Designing policies for the sustainable development of social-ecological systems with complex human–land relations requires integrated management and nexus thinking; China’s national parks are typical social-ecological systems. Ecosystem services and community livelihood are two essential components of sustainable management in the nature–community nexus (NCN). This study focuses on the Qianjiangyuan National Park Pilot Area in eastern China. Following a systems approach and integrating qualitative (causal analysis and systems but dynamic methods) and quantitative (InVEST model, Spearman’s correlation analysis, regression analysis, and multiple correspondence analysis) methods, we developed two causal mechanisms linking livelihood assets and ecosystem services, and verified them by exploring multi-dimensional linkages and revealing two types of NCNs. Results showed that the proportions of cropland and orchard areas have significant negative correlations with water and soil retention services, respectively, while forests significantly benefit both services. A positive NCN exists in areas where water and soil retention services perform well and the local community develops vibrantly with a considerable proportion of young, highly educated, or high-income (especially the income from secondary industries) residents. A negative NCN is seen in areas where the water and soil retention services values are low; a great many households do not have substantial income from secondary and tertiary industries, and few households have vast forest areas. These results can be used as scientific evidence for optimizing institutional arrangements and contributing to sustainable and harmonious development of national parks in China.