在区域创新协同背景下，城市创新网络的构建对于提升区域创新能力、实现区域协调发展具有重要意义。特别是在“双碳”目标下，经济低碳化发展催生了对低碳创新的需求。中国不同城市之间的低碳创新联系日益活跃，低碳创新网络不断完善，交通基础设施的建设对低碳创新网络结构的影响值得探讨。本研究采用社会网络分析法构建我国长江三角洲地区2000-2020年城市低碳创新网络，分析网络密度、节点中心度、凝聚子群等结构特征的时空规律；基于多期双重差分模型和多元线性回归模型研究高速铁路开通对长三角地区低碳创新网络结构的影响及其机制。研究的主要发现为：（1）我国东部地区低碳技术创新水平明显高于中西部地区，其中长三角地区具有相对活跃的低碳技术创新与相对均衡协调的低碳技术合作创新空间格局；而且长三角地区低碳创新重要性不断提升，低碳合作创新在所有合作创新中占据越来越重要的地位。（2）2000-2020年，长三角地区低碳创新合作网络不断完善，呈现跨区域组团发展格局，网络权力趋于分散，均衡发展态势较明显，其中上海、南京、杭州成为其内部的重要节点。2020年整个长三角地区形成上海、南京、杭州“三足鼎立”的低碳创新发展格局，但是随着时间的推移，上海的主体影响地位在弱化，南京和杭州发展迅速。各个节点城市在网络中的中介控制作用的差异也在逐渐缩小。上海市、江苏省和浙江省的城市在低碳创新网络中更接近中心位置，不受束缚的能力相对较强。（3）高铁的建设对低碳创新合作发展和区域创新网络的构建具有十分重要的作用。高铁的开通和建设有效提升了当地低碳创新合作水平，促使高铁城市与更多的对象进行创新合作，大大提升了高铁城市在创新网络中的中心性和中介调节作用。这一结论在人口规模相对较小的城市中更加明显；对超大型城市来说，高铁开通使其核心地位更加稳固。机制分析表明，高铁的开通和建设通过促进高新技术企业、风险投资和创新人才在当地的集聚，从而提升低碳创新合作水平和节点中心性。未来，各个地区和城市应该持续完善高铁网络建设，将高铁与社会经济发展深度融合，促进城市间创新要素流动和一体化发展。中小城市更应该抓住高铁发展的机遇，提升自身在创新网络中的地位。

Under the background of regional innovation collaboration, the construction of urban innovation network is of great significance for improving regional innovation ability and realizing regional coordinated development. Especially in the context of carbon neutrality and carbon peaking, low-carbon economic development has created a need for low-carbon innovation. The low-carbon innovation links between different cities in China are increasingly active and the low-carbon innovation network is constantly improved. The influence of the construction of transportation infrastructure on the low-carbon innovation network structure is worthy of discussion. In this study, social network analysis method was used to construct the urban low-carbon innovation network in the Yangtze River Delta during 2000-2020. The spatial and temporal patterns of network density, node centrality, cohesive subgroups and other structural characteristics were analyzed. Based on the multi-period differences-in-differences model and multiple linear regression model, this paper studies the impact of high-speed rail on the structure of low-carbon innovation network in the Yangtze River Delta. The main findings are as follows: (1) The innovation level of low-carbon technology in eastern region is obviously higher than that in Midwest region. The Yangtze River Delta region has relatively active low-carbon technology innovation, and the spatial pattern of low-carbon technology cooperation innovation is also relatively coordinated. The importance of low-carbon innovation in the Yangtze River Delta is increasing, and low-carbon cooperative innovation is playing an increasingly important role in all cooperative innovation. (2) From 2000 to 2020, the low-carbon innovation cooperation network in the Yangtze River Delta has been continuously improved, showing a cross-regional development pattern with decentralized power and an obvious trend of balanced development, among which Shanghai, Nanjing and Hangzhou have become important nodes within the network. By 2020, the whole Yangtze River Delta region has formed a low-carbon innovative development pattern featuring Shanghai, Nanjing and Hangzhou. However, with the passage of time, Shanghai's dominant influence was weakening, while Nanjing and Hangzhou developed rapidly. The difference of the intermediary control role of each node city in the network is also gradually narrowing. Shanghai and cities in Jiangsu and Zhejiang provinces are closer to the center of the low-carbon innovation network and relatively strong in their ability to be unfettered. (3) The construction of high-speed railway plays an important role in the development of low-carbon innovation cooperation and the construction of regional innovation network. The opening and construction of high-speed rail has effectively raised the level of local cooperation on low-carbon innovation. It promotes the innovation cooperation between high-speed rail cities and more objects, and greatly enhances the centrality and mediating role of high-speed rail cities in the innovation network. This is especially true in cities with relatively small populations. For the megacities, the opening of high-speed rail makes their core position more secure. Mechanism analysis shows that the opening and construction of high-speed rail can improve the level of low-carbon innovation cooperation and node centrality by promoting the local agglomeration of high-tech enterprises, venture capital and innovative talents. In the future, all regions and cities should continue to improve the construction of high-speed rail networks, deeply integrate high-speed rail with social and economic development, and promote the flow of innovative factors and integrated development among cities. Small and medium-sized cities should seize the opportunity of high-speed rail development to improve their position in the innovation network.