The construction of smart cities is an important choice for the high-quality and sustainable development of Chinese cities in the future, and it is also an important way for China to promote new industrialization and develop new quality productivity at the current stage. Combining the technology centrism and humanism of smart city construction, and constructing indicators of smart city elements from capital, people, technology, and space, this article explains the mechanism by which intellectual capital affects and promotes the economic growth of smart cities through four major ways including human quality, intellectual output, technology investment, and openness level. And using panel data from 2002 to 2022, a production function model is constructed to analyze the impact of intellectual capital in 11 core cities of the Yangtze River Economic Belt on the economic growth of smart cities. The research results indicate that there are commonalities and characteristics in the future development of different smart cities. The agglomeration of intellectual capital in the Yangtze River Economic Belt has a significant promoting effect on the economic growth of smart cities, and its decomposition factors have heterogeneous effects on the economic growth of smart cities in different regions and at different levels. The level of openness is currently the most important factor. On this basis, countermeasures and suggestions are proposed for the future development of smart city economy in the Yangtze River Economic Belt. We should start from the construction of digital twin cities, the digital development of industries, and the aggregation of digital transformation factors, and implement smart city development strategies guided by different regional and hierarchical city classifications. Guided by the market demand for smart city construction, we should focus on the market transformation of intellectual output, and leverage the influence and driving role of intellectual capital. We also need to promote the effective integration of various elements of intellectual capital, strengthen the integration of “technology + humanism”, and promote the cross-domain circulation of data elements.