The city's leading industries are the core of the city's industrial structure upgrading and economic pattern optimisation. In order to effectively identify the dominant industries in cities, a dominant industry identification method based on industrial ripple effect, industrial growth potential and regional comparative advantage is constructed, and the TOPSIS method is used to determine the dominance of each dominant industry. The kernel density and standard deviation ellipse methods are used to study the industrial agglomeration of the identified dominant industries. Taking Ningbo as an example, three dominant industry sectors are identified and ranked in order of their dominance: industry, transport, storage and postal services, and business services. Further analysis of the most dominant industry is carried out to identify five industrial sub-sectors, which are ranked as follows: automobile manufacturing, chemical raw materials and products manufacturing, electrical machinery and equipment manufacturing, non-ferrous metal smelting and calendering, and instrumentation manufacturing. The results of the industrial agglomeration analysis show that transportation, storage and postal services, and business services are mainly concentrated and distributed within the main urban area of Ningbo, the leading industries in the five industrial sub-sectors are mainly concentrated and distributed within the main urban area in central Ningbo and two county-level cities of Yuyao and Cixi in the north.