Abstract: Improving the efficiency of green development and narrowing the regional gaps are essential ways to promote mountainous counties to move towards common prosperity. The super-efficiency SBM model and the Theil coefficient were used to measure the green development efficiency and regional gaps of 26 mountainous counties (cities, districts) of Zhejiang Province from 2010 to 2022. The future development trend of green development efficiency was discussed by combining NICH index and Hurst index, and the panel Tobit model was used to identify the driving factors of green development efficiency. The results showed that: (1) During the study period, the overall green development efficiency of 11 ecological development counties was always higher than that of 15 leapfrog development counties, and the regional differences in green development efficiency had gradually narrowed. (2) The spatial convergence distribution was quite different. The bottom-divergent counties changed from low-level block aggregation to point-like dispersion; the bottom-convergent counties transitioned from banded distribution to block agglomeration; the top-convergent counties transferred from the central and western regions to the east; the top-divergent counties were relatively scattered. (3) In the foreseeable future, the green development efficiency of Jingning She Autonomous County, Panan County, and Qingtian County was projected to experience steady and efficient growth. Conversely, Liandu District, Longquan City, and Suichang County were anticipated to witness marked declines, characterized by low sustainability and stability in their green development endeavors. (4) Urbanization and industrial structure were the main factors to improve the overall green development efficiency of 26 mountainous counties (cities, districts). For ecological development counties, the improvement of industrial structure can significantly improve their green development efficiency. For leap-forward development counties, urbanization is the key to improving their green development efficiency.