Abstract: In recent years, China's technological innovation strength has made significant progress, but it still faces problems such as weak basic research and original innovation capabilities, lack of key core technologies, and disconnection between innovation and industry. The reasons for these problems are complex, and the insufficient development of technology intermediaries may be one of the important reasons. Technology intermediaries play an important role in urban innovation and development. The National Technology Transfer Regional Center (NTTC) is a high-level technology intermediary and an important component of the national technology innovation system. As of August 2023, China has built 12 NTTCs, and the construction effectiveness of these NTTCs has always been a concern. Based on the panel data of 278 prefecture-level and above cities in China from 2010 to 2021, this paper uses the staggered difference-in-difference model to conduct an in-depth examination of the causal relationship and key mechanisms between technology intermediaries represented by NTTC and urban innovation. The results show that NTTC significantly promotes the improvement of general and core technological innovation levels in the city, but more importantly, it promotes the improvement of general technological innovation levels in the city. The government support effect, innovation factor inflow effect, and enterprise agglomeration effect are the key mechanisms of NTTC promoting the improvement of urban innovation level. NTTC has a spatial spillover effect of “∽” type on the innovation level of surrounding cities, which can promote the improvement of innovation level in cities within suitable distances, but has no significant impact on cities in closer or farther distances. The regional characteristics and administrative levels of a city can lead to differences in the improvement effect of NTTC on the level of urban innovation. This paper has the following policy implications. First, the government should continue to strongly support the construction of NTTC, actively promote the construction of various types of technology intermediaries while ensuring the quality of existing NTTC construction. Second, the government should strengthen policy support, optimize the foreign investment and business environment, fully amplify the government support effect, innovation factor inflow effect, and enterprise agglomeration effect of NTTC establishment, and assist urban innovation and development. Third, the government should implement a differentiated technology intermediary construction strategy, making technology intermediaries an important support for bridging the regional innovation gap. This paper may have the following marginal contributions: (1) Distinguishing from the existing literature on technology intermediaries, this paper focuses on technology intermediaries represented by NTTC and urban innovation, emphasizing the causal relationship between the two to enrich the existing research.(2) In addition to testing the policy effect of NTTC, this paper also discusses the key mechanism of NTTC on urban innovation level from theoretical and empirical analysis, which helps to clarify the internal logic of technology intermediary affecting urban innovation.(3) The conclusion of this paper may have reference value for the government to optimize the construction of technology intermediaries, and it is also of great significance to improve the national technology innovation system and accelerate the realization of self-reliance science and technology.