Abstract: Using a sample of 41 cities in the Yangtze River Delta city cluster, a dynamic panel measurement econometric model is constructed using panel data from 2009-2018, and a systematic GMM approach is used to empirically analyze the effects of specialization and diversification on the economic growth of cities within the Yangtze River Delta city cluster. It is found that industrial specialization is conducive to promoting urban economic growth. There is an inverse “U” non-linear relationship between the degree of specialization and industrial growth. Industrial diversification is not conducive to promoting urban economic growth. There is a positive “U” non-linear relationship between the degree of diversification and industrial growth. There is a positive U-shaped nonlinear relationship between the degree of diversification and industrial growth. Therefore, the city's industrial development strategy needs to be based on its own characteristics and moderate adjustment of industrial structure; the city's industrial layout needs to find a foothold in the Yangtze River Delta industrial symbiosis network and jointly promote the integrated high-quality development of the Yangtze River Delta.