The Third Plenary Session of the 20th CPC Central Committee has conducted in-depth research on further comprehensively deepening reform and promoting Chinese-style modernization. Its issues and decisions have a positive impact on promoting the unified national market and improving the new quality productivity, so as to promote high-quality economic development. Based on the panel data of 226 prefecture-level cities in China from 2012 to 2022, the influence of the development level of China’s new quality productivity on the construction of unified national market is deeply analyzed through the intermediary effect test. The research results show that the new quality productivity has a positive impact on the construction of unified national market. The higher the development level of new quality productivity, the greater the degree of market segmentation inhibition, and the faster the construction and development of unified national market. This positive effect is particularly significant in eastern and northeastern regions, non-provincial capital cities and non-resource-based cities. New quality productivity promotes the construction of the unified national market through the optimization of industrial structure and business environment. Finally, this research reveals the key role of the development level of new quality productivity in promoting the development of the unified market, and provides theoretical support and important reference for the high-quality economic development.