•Revisit the relationship between population and energy in the late stage of demographic dividend.•Consider the relationship between population and energy from the perspective of metabolism.•Measure metabolic efficiency by combining emergy analysis and the Index-DEA.•Explore the multi-scale response of metabolism to population quality.•Provide a reference for other developing countries with population and energy issues. China's population and carbon emissions will reach two peaks in 2030. Especially in the late stage of demographic dividend, it is necessary to revisit the relationship between population and energy. Metabolism is a critical perspective to help understand the population-energy relationship. This paper establishes a new paradigm for assessing the impact of population quality change on regional metabolism based on panel data from 2003 to 2019 in China. We measure the population quality index (PQI) using the Projection Pursuit method from four aspects and regional metabolic efficiency (RME) using emergy analysis and Index-DEA. Then, the Tobit model is used to explore the impact of population quality change on regional metabolism from a multi-scale perspective. The results show that the influence has some variability at different scales. From the total sample, the response of regional metabolism to population quality is significantly positive. For different PQI regions, the RME has a positive response to PQI in both, but this response is more obvious in advanced PQI regions. For regions in different locations, RME has positive response to PQI in both East and West, but there is no obvious response in the Central. These findings are closely related to global sustainable development.