The rise of urban agglomerations is an important symbol of economic development to a certain stage, and at the same time constitutes a huge driving force for economic development. Based on the panel data of Chinese cities from 2003 to 2017, this paper empirically tests the impact of national-level urban agglomeration construction on green innovation by means of using DID and other methods. The marginal contribution of this study lies in: evaluating the short-term effects of national-level urban agglomeration construction on green innovation; examining the similarities and differences between the impact of national-level urban agglomeration construction on green productivity and on green patents; analyzing the pathway of national-level urban agglomeration construction impacting on green innovation basing on intermediary mechanisms such as factor mobility and policy strictness. The study found that the construction of national-level urban agglomeration has a significant positive impact on green productivity, but has no significant impact on green patents. Therefore, it can be seen that the impact of urban agglomeration construction on green productivity and on green patents is heterogeneous. The strong Porter hypothesis is tenable while the weak Porter hypothesis is not, which means that the construction of national-level urban agglomeration promotes green efficiency rather than green technological progress. After adopting a series of robustness tests such as PSM-DID, counterfactual analysis, cluster standard deviation regression, dynamic panel regression and instrumental variable regression, it proves that the result is robust. Based on the heterogeneity analysis, it is found that the construction of national-level urban agglomeration has a significant positive impact on the green productivity of medium-tech, low-tech and peripheral cities, but has no significant impact on the green productivity and green patents of high-tech and central cities.
