China is currently undergoing a critical transition in its demographic and economic structure. As a fundamental driver of economic and social development, demographic changes may significantly influence the transformation of the industrial structure. Therefore, examining the impact and mechanisms of population ageing on the restructuring of China's industries holds substantial practical importance. By constructing mathematical models and conducting empirical analyses based on provincial panel data from 1998 to 2023, this study finds that population ageing exerts a significant negative effect on the development of the secondary industry, a significant positive effect on the tertiary sector, and a notably positive influence on overall industrial structural transformation. Further analysis of mediating effects reveals that, during the observation period, population ageing accelerated industrial structural transformation through the labor supply scale effect and the consumption structure effect, while simultaneously decelerating the process via the labor productivity effect and the consumption scale effect. It is imperative to promote the development of the tertiary sector especially the producer services, sustain and enhance labor-intensive service industries, and simultaneously accelerate the growth of medium-and high-end manufacturing.