Abstract: As an important part of new infrastructure construction, the UHV transmission project not only undertakes the important responsibility of regulating energy supply and demand, but also the historical mission of regional environmental optimization. Based on the panel data of 1,625 counties and districts from 2003 to 2020, this paper conducts a study by employing the staggered double-difference method. The results show that the UHV transmission project can significantly reduce regional PM concentrations, thus contributing to the optimization of the regional environment. Specifically, counties and districts that commissioned UHV transmission projects reduced their PM concentrations by about 1.51 percentage points on average compared to those that did not. UHV transmission helps optimize the regional environment through three mechanisms: optimizing resource allocation, promoting cleaner production and facilitating green innovation. There is significant spatial heterogeneity in the environmental effects of UHV transmission projects. On the one hand, UHV transmission project significantly suppresses PM concentrations in power importing places, the eastern regions and the regions with relatively scarce energy resources; on the other hand, it exacerbates the environmental pressure in power exporting places, the western regions and the regions with abundant energy resources to varying degrees. Therefore, in the construction of UHV transmission projects, the state should focus on the welfare of the residents and the ecological environment issues in the power exporting areas, the western areas and the resource-rich counties, and establish a sound system of ecological compensation and technical support to realize a two-way balance between economic development and environmental protection.

Key words: UHV transmission, resource allocation efficiency, regional environmental optimization, staggered difference-in-differences, heterogeneity bias diagnosis