Abstract: China has entered a new stage of high-quality economic development. Green development is undoubtedly a necessary requirement to promote high-quality economic development in the new era, among which the transformation and upgrading of manufacturing industry play a crucial role. Based on China’s provincial panel data, this paper empirically explores the impact mechanism of manufacturing agglomeration on green development, the conditions for upgrading and the spatial effect. The results show that: (1) the manufacturing agglomeration in the whole country, eastern, central and western regions can significantly promote the green development of the region and the improvement of technical progress and technical efficiency. (2) From the meso perspective, open trade, industrial structure upgrading and human capital are the effective transmission paths of manufacturing agglomeration on green development. (3) The impact of manufacturing agglomeration on green development shows a trend of “increasing marginal effect” with the increase of human capital, industrial structure upgrading and green technology innovation. (4) China’s manufacturing agglomeration and green development present a trend of “higher in the east and lower in the west”, and the two have shown a positive spatial correlation in recent years, and continue to extend to the inland areas through the learning effect year by year. (5) The manufacturing agglomeration has a significant negative spatial correlation with green development, and the improvement of the manufacturing agglomeration level in the “neighbor” region will inhibit the improvement of the local green development level.