Building on the “pragmatic” criterion of economic growth and the evolutionary perspective of the rank-size power law distribution, this study constructs a theoretical framework to analyze how the evolution of urban hierarchy influences urban economic growth. Taking China’s Bohai Rim Megalopolis as the research subject for the period 2003－2016, it investigates the optimal urban hierarchy influencing urban economic growth, aiming to provide theoretical insights and decision-making support for policies that promote coordinated economic development in Megalopolis.The study shows that an optimal rank-size power-law distribution exists within the urban system that promotes economic growth, yet this optimal distribution does not align with the configuration implied by “Zipf’s Law”. The extent to which increased urban infrastructure stock can positively moderate the spatial concentration of city sizes and thereby promote economic growth is constrained by the efficiency of market mechanisms in resource allocation. Achieving an optimal spatial distribution of city sizes within an urban system hinges on effective government regulation that enables the market mechanism to play a decisive role in resource allocation. This study enriches the theoretical comprehension of the spatial distribution of urban size within urban systems. The findings provide substantial theoretical references and policy implications for promoting China’s strategy of clustered and networked urban development and facilitating coordinated urban growth.