The emergence of new urban enterprises, new capital and new inventions is the source of vitality to breed the core technologies of emerging industries, and has great significance to accelerate the formation of new quality productivity. This paper uses the panel data of Chinese cities to investigate the impact of innovation and entrepreneurship vitality on core technologies of emerging industries and the mechanism of action. The research finds that: (1) Urban innovation and entrepreneurship vitality significantly promotes the increase of core technologies of emerging industries, and the conclusion remains valid after considering a series of robustness tests. (2) The influence of innovation and entrepreneurship vitality on core technology activities of emerging industries has a threshold feature of “marginal increase” of city size, and has a significant inhibitory effect on neighboring cities, with “Matthew effect” and “siphon effect”. (3) The influence of innovation and entrepreneurship vitality on core technology activities of emerging industries has regional and gradient heterogeneity. There are significant differences between cities in different geographical locations and cultural regions, and the group regression of resource-based cities, smart cities and innovative cities reflects gradient characteristics. (4) Innovation and entrepreneurship vitality promote the growth of core technologies in emerging industries by enhancing the diversity of cities, especially the diversity of specialized sectors.