Abstract: As the cornerstone of digital economy development， digital infrastructure plays a critical role in promoting China's economic growth and enhancing the quality of foreign trade. Based on panel data from 263 cities in China from 2010 to 2020， this study treats the “broadband China” demonstration city construction policy as a quasi natural experiment and employs a progressive double difference model to analyze the mechanism and impact effect of digital infrastructure construction on the high quality development of foreign trade. The research finds that the “broadband China” demonstration city construction policy significantly promotes the high quality development of foreign trade， and this promotional effect becomes more evident over time， remaining valid after a series of robustness tests. Heterogeneity analysis results indicate that the promotional effect of digital infrastructure on the high quality development of foreign trade varies by region and city size， with a more significant impact on eastern cities and larger cities. Mechanism testing shows that digital infrastructure promotes the high quality development of foreign trade by enhancing urban technological innovation and deepening marketization. Based on these findings， government departments should actively improve urban digital infrastructure construction， enhance urban innovation levels， and build a unified domestic market to support the high quality development of foreign trade.

Key words: digital infrastructure, “broadband China”, high-quality development of foreign trade

摘要： 作为数字经济发展的基石，数字基础设施的完善对推动中国经济发展、外贸质量提升起到关键作用。基于中国2010—2020年263个城市的面板数据，将“宽带中国”示范城市建设政策作为一项准自然实验，采用渐进双重差分模型，分析数字基础设施建设对外贸高质量发展的作用机制及其影响效应。研究发现：“宽带中国”示范城市建设政策对外贸高质量发展有显著促进作用，且随着时间的推移促进作用更加明显，在一系列稳健性检验后结论依然成立；异质性分析结果表明，数字基础设施对外贸高质量发展的促进作用存在区域差异和城市规模差异，对东部城市、较大规模城市的作用更显著；机制检验显示，数字基础设施通过提高城市技术创新和加深市场化程度促进外贸高质量发展。基于此，政府部门应积极完善城市数字基础设施建设，提升城市创新水平，建设国内统一大市场，助力外贸高质量发展。

关键词: 数字基础设施, “宽带中国”, 外贸高质量发展