China is currently at a critical stage in transitioning from a large petrochemical country to a powerful one. To clarify the relationship between the development of the petrochemical industry and local ecological economy and explore the scientific development path for the industry, this paper analyzes the influence of petrochemical industry agglomeration on local ecological efficiency. By using panel data from 30 provincial units between 2012 and 2021, the study also investigates the mediating effect of green technology innovation on this relationship. Results show that the agglomeration of China’s petrochemical industry positively affects local ecological efficiency. However, given some issues such as separation of production and innovation activities within the industry, a negative correlation exists between the agglomeration level of the petrochemical industry in China and the level of green technology innovation. Consequently, the agglomeration of China’s petrochemical industry cannot enhance ecological efficiency through the mediating effect of green technology innovation level. The substantial resource consumption by green technology innovation has not translated into effective ecological economic benefits, which has increased the burden on ecological functions and resulted in a negative effect on ecological efficiency. The research conclusions and proposed measures hold significant implications for the scientific planning of the development of China's petrochemical industry, as well as for promoting regional economic growth and ecological construction.