The Yangtze River Delta urban agglomeration is the central area driving the high-quality development of the Yangtze River Delta，the leading area of regional integration of the Yangtze River Delta，and also an important functional area in the domestic regional economy and opening-up pattern of China. Based on the data of statistical yearbook and bulletin，this paper mainly analyzes the economic development of the whole，sub regional and core cities in the Yangtze River Delta urban agglomeration. The main conclusions are as follows：In recent years，the overall regional economy of the Yangtze River Delta urban agglomeration has shown a downward trend. In 2019，its average economic growth rate was further reduced，but it was higher than that of the whole Yangtze River Delta，the whole country and the world. Regional GDP keeps increasing. In 2019，it exceeded 20 trillion yuan，playing a decisive role in supporting the economy of the Yangtze River Delta and an important role in the national economy. The economic development level of urban agglomeration improved steadily，and the main indicators are better than the Yangtze River Delta and the whole country. The population of the urban agglomeration continued to increase，and the urbanization rate rose rapidly. The economic operation trend among cities in Yangtze River Delta urban agglomeration was different. But economic growth rate of most cities slowed down. The regional GDP，population and economic development level have all improved，but the regional gap is a little large. The core cities of the urban agglomerations show strong development resilience and leading advantages，but their development stages are different.