Abstract:     In the context of comprehensive green transformation development of Chinese economy and society, new urbanization led by smart cities is an important strategic choice to alleviate urban diseases and improve ecological environment. At the same time, green technology innovation as an important path to realize the coordinated development of economy and environment, it is necessary to examine the impact of smart city construction on green technology innovation. However, most of the existing studies examine the impact path of smart city construction on technology innovation from the macro level, lacking in-depth investigation of the mechanism of action at the micro level. In addition, existing studies lack the examination of the policy spillover effects of smart city construction, which makes it difficult to provide useful references for the promotion of smart city pilot experiences.
   Based on the micro-data of Chinese listed companies from 2010 to 2018, this paper empirically-tested the impact, mechanism and spillover effect of smart city construction on enterprise green technology innovation by using Differences-in-Differences. The results are as follows: First, smart city construction can significantly promote enterprise green technology innovation, and compared with high-quality green technology innovation, smart city construction has a more significant promoting effect on low-quality green technology innovation. After a series of robustness tests, this result still holds. Second, the impact of smart city construction on enterprise green technology innovation has a positive policy spillover effect within the province. The higher the quantity and quality of pilot cities within the province, the fiercer the resource competition between advanced cities and catch-up cities, thus forming a phenomenon of "top-to-top competition" among cities around enterprise green technology innovation. Third, smart city construction can significantly promote enterprise green technology innovation by promoting enterprise digitization, increasing R&D investment and environmental protection expenditure.
    Based on the above research conclusions, this paper obtains the following implications: first, local governments should vigorously promote urban infrastructure construction and the deeply integrated development of digital technology, provide favorable support for the diffusion and absorption of innovative knowledge and the transformation of innovative results, break the data island, and promote enterprises to make higher quality green technology innovation. Second, the government should unswervingly promote the construction of smart cities in the way of pilot first, actively promote the advanced development experience of pilot cities, give play to the positive demonstration effect of smart city pilot policies on other cities, and promote the green technology innovation of enterprises through the virtuous cycle of smart city development. Third, the government should attach importance to the application of digital technology at the enterprise level and reduce the barriers to knowledge sharing of innovation among enterprises. Enterprises should take smart city construction as an opportunity to innovate their business operation mode and reduce their R&D risks and operating costs. Finally, green development content such as smart environmental protection and smart energy should be strengthened to force enterprises to increase investment in green technology innovation.

Key words:  smart city, green technology innovation of enterprises, DID estimation