Low-carbon urban development has been regarded as a promising is hot spot of global concern on fighting pathway for mitigatingto climate change, whileand transportation sector as a key role contributes takes a significant proportion to the total CO2 emission. Investigate Investigating the driving factors and analyzing the causal mechanism on urban transport CO2 emission is critical for the stakeholders/policy-makers to draft appropriate policies for low-carbon transport its ever-improvement, and conducting comparative study on developed and developing countries’ experience will provide beneficial insights from an evolving perspective. Up to date, there are many emerging case studies on the analysis on urban transport CO2 emission in China; however it, but lacks in-depth decomposition and causal mechanism analysis, as well as comparative study. Under this circumstanceIn order to fill this gap, this research study aims to conduct a decomposition analysis and causal mechanism investigation study on urban transport sector, with comparative studies on two Asian mega cities named Tokyo , Japan and Shanghai, China. We illustrate the driving forces of urban transport sector and the causal mechanism of each factor, and provide critical policy insights through comparative studies. The outcomes of this study provide critical insights to the recent practice in Shanghai, as well as the practical guidance to low carbon urban planning in developing countries.