Urban network research has become the frontier academic field of international urban research and has gradually become a hot spot. At present, the related literature on "urban network" mostly focuses on conceptual discussion, dimension analysis, and network structure analysis. Research on the influence of network on regional economic development is relatively weak. Externality, as an essential attribute of urban network, is of great significance to the evolution of urban network and the development of cities and regions. This article starts from a comparison of agglomeration externalities with urban network externalities, focusing on the review and evaluation of the formation mechanism, utility, and measurement methods of urban network externalities. The synergy effect, integration effect, and borrowing size are considered important reasons for the formation of urban network externalities. The research on the effectiveness of urban network externalities focuses on two aspects. The first is the role of factor flow in promoting knowledge diffusion and innovation, and the second is the impact of urban network on competitiveness and economic growth. Based on the existing literature, the research on the measurement of urban network externalities mainly involves identification and estimation, including three common methods: correlation analysis, regression analysis, and spatial econometric analysis. The existing empirical research on externalities is still mostly based on static analysis and lacks dynamic consideration. To a large extent, the existing research has insufficient theoretical framing and insufficient explanatory power, often resulting in the discovery of conditional associations, but not causal relationships. The Western research on urban network externalities is relatively early and mainly focuses on the global and regional dimensions, while Chinese scholars focus on the national and regional dimensions. In terms of empirical methods and objects, Chinese scholars have also made some innovations based on the study of world city network. The issues that need further attention in the future include theoretical understanding of urban network externalities, externality measurement methods, and empirical research.
