Low-carbon energy system is a proactive option, which aims at energy efficiency, clean utilization and large-scale renewable energy consumption as the background. It is composed of multiple types of energy systems and realizes the organic coordination of production, transmission, distribution, transformation, storage, consumption and other links of different energy forms in multiple space-time scales. This report aims at a better understanding of the low-carbon energy system concept, ideas, advanced technologies, models and application forms; so as to help cities improve the energy efficiency and contribute to cities’ sustainability, as well as how cities take the road of sustainable development in the APEC region.