How can small and medium-sized cities differentiate their carbon peaks?

China's ‘dual carbon’ strategy is of strategic importance in leading global climate governance and promoting China's high-quality and green economic development. Cities are the centres of human activities. However, these are also places where high energy consumption and high carbon emissions are concentrated. This study selected data from 192 small and medium-sized cities in mainland China for the period 2000–2020. It classified these into seven categories using the K-means clustering method, calculated the decoupling status of different types of small and medium-sized cities based on the Tapio decoupling index, and analysed the relationship between carbon emissions and economic growth in various types of small and medium-sized cities based on the EKC curve theory. Finally, the backpropagation neural network (BPNN) model was used to classify and predict the time required to achieve carbon peaking for seven types of small and medium-sized cities. The following conclusions were drawn: (1) The development status of small and medium-sized cities shows a ‘geese echelon pattern’. New dynamic small and medium-sized urban areas may reach peak carbon emissions first, while resource-based small and medium-sized urban areas may be the last to do so. (2) The decoupling of carbon emissions from industrial development in small and medium-sized cities has not been completed. This manifests mainly through the states of declining decoupling, absolute decoupling, and strong negative decoupling. (3) A significant inverted U-shaped relationship exists between economic development and carbon emissions in these cities. (4) These cities may have the disadvantage of premature or excessive de-industrialisation. Additionally, these generally have an inefficient and expansionary economic development status. Therefore, this study contended for a more robust integration of a radical political economy and ecological economics to support the development of such cities in China. The paper proposes differentiated development paths and fundamental recommendations for small and medium-sized cities in the implementation of the ‘double carbon’ strategy. The intention is to provide theoretical guidance and implications for promoting green and low-carbon development in urban and rural areas and for the early achievement of the strategy in China.