The technical default of urban investment?bonds and the default of urban?investment companies' non-standard financing have broken the long-standing “belief” in the rigid payment of urban investment?bonds, and the credit risk has become the focus of attention. Under the background of the implementation of the urban agglomeration strategy in China, based on the gravitational network of production factors within the Yangtze River Delta Urban Agglomeration, this paper empirically analyzes the impact of urban agglomeration spatial spillover on the credit risk of urban investment bonds. The study finds that: 1) There is a spatial overflow of credit risk within the urban agglomeration, and the credit risk premiums of urban investment?bonds in different cities fluctuate in the same direction. 2) The financial development of other cities especially peripheral cities is positive externality, which can reduce the risk. 3) There may be negative externalities in the economic development of urban agglomerations especially the peripheral cities, which will increase the credit risk. It provides a theoretical and factual basis for local governments to make effective use of the development opportunities of urban agglomeration, reasonably formulate fiscal policies and prevent and control regional financial systemic risks.