Understanding the nexus between socioeconomic factors and urban carbon footprint can help a city devise carbon reduction strategy and achieve its sustainable development. The multi-scale input-output method is combined with structural decomposition analysis in the present work to analyze the changes and driving forces of a city’s consumption-based carbon emissions. It is for the first time to include import as one of the major underlying socioeconomic variables. A case study is carried out to analyze Shanghai’s consumption-based carbon emissions in 2007 and 2012. According to the results, the consumption-based carbon emissions of Shanghai have risen by 32.82% since 2007, which grew much faster than the production-based carbon emissions. The carbon emissions trade of Shanghai has almost doubled during the period. While Shanghai’s net domestic carbon emissions import has increased by 20%, the net international carbon emissions export has decreased by half. The domestic import change and consumption per capita change were the main drivers for the growth in consumption-based carbon emissions of Shanghai during 2007–2012. At the meantime, technology change and international import change helped a lot to reduce carbon footprint of Shanghai.