Controlling carbon emissions without impairing urbanization and economic development highlights the necessity of researching energy-related carbon emissions. Urban areas have become the main source of energy consumption and carbon emissions. This paper has developed a modified version of the Kaya identity, which incorporates urbanization and resident consumption, to analyze urbanization effect on carbon emissions in Jiangsu Province. Then, the Kuznets curve theory was introduced to estimate the inflection point of the marginal urbanization effect. The results indicated that the urbanization effect was still an important factor that influences total carbon emissions. The marginal urbanization effect will still increase until the urbanization rate reaches 78.94%. Therefore, Jiangsu should also pay attention to the urbanization effect even though it may increase slowly or decrease, and the results of this paper on marginal urbanization effect make it clear that controlling the carbon emissions without the expense of urbanization growth and economic development is still a big challenge for Jiangsu Province. We have proposed some policy recommendations, which include paying attention to the quality of development of urbanization, adjusting the industrial structure, making changes to lifestyles, and so on.