Better modeling of urbanization trends helps improve our understanding of the potential range of future energy demands and carbon dioxide emissions in developing countries and make informed response strategies. This paper extends the current analytical structure by integrating the population migration process from rural to urban areas with the energy system into a systematic framework, within which a link between urbanization and energy service demands through direct and indirect effects is built. Taking China as a study case, the results show that approximately 333 million people from rural areas are expected to migrate to urban areas toward 2050, resulting in the expansion of large-sized cities and the rapid growth of future energy service demands. Without significant technological improvements, urbanization will lead to more than double and triple the current energy consumption levels by 2050 in the building and transport sectors, respectively, while energy consumption growth in the industry sector will be the largest due to the rising demand for materials through the indirect effect. As a result, urbanization in China will cause more than double the total primary energy demand and an 82% increase in the carbon dioxide emissions by 2050, compared with 2013. In response, major mitigation measures and the role of each sector in the low carbon urbanization transition have been identified. Non-fossil fuel power generation is the top mitigation strategy, which can contribute 40% to the total mitigation potential, while power sector and industrial sector play a key role in realizing an earlier peak for the whole country. The total capital investment needed in each period will cost less than 2.5% of the total gross domestic product (GDP). Therefore, this work highlights the importance of understanding urbanization impact on energy system through applying an integrated population-energy-environment analytical framework and synthesizing the urbanization and long-term low carbon strategies in developing countries which are under rapid urbanization process.