本文基于青藏铁路全线开通这一准自然实验，采用双重差分模型，利用2003-2020年青藏地区的面板数据，分析了青藏铁路开通对沿线地区经济、社会和文化发展的影响效应和作用机制，并运用平行趋势检验、随机抽取处理组和工具变量法等稳健性检验方法验证了研究结论。双重差分法能够克服由于变量内生性、遗漏变量等对模型估计产生的偏误，更有效地评估青藏铁路开通运营的外部性。研究发现：总体上，青藏铁路开通显著提升了沿线地区人均GDP，缩小了城乡居民收入差距，并增加了文化企业数量和旅游总收入。机制研究发现，青藏铁路分别通过拉动投资与发展服务业、促进就业、提高人口流动性与旅游吸引力推动沿线城市经济、社会和文化发展。异质性分析发现，青藏铁路产生的经济效应、社会效应和文化效应对沿线非中心城市的有利影响较大。上述发现表明，青藏铁路有利于青藏地区实现结构转型与共同富裕，且其经济、社会和文化效应短期内具有持续性。本文提供了重大铁路工程外部性的定量评估分析框架，为推动类似重大工程项目高质量发展以及区域可持续性和谐发展提供理论支撑。

Mega-railway projects hold a crucial position in developing and constructing a strong transportation network in China. Existing methods to quantitatively analyze and evaluate externalities of these mega-railway project are currently inadequate， and quantitative based studies on the externalities of mega-railway projects has important theoretical and practical implications for the sustainable development. Three key questions， i.e. what is the impact of the opening of Qinghai-Tibet Railway on the regional economy， society and culture development？ What is the mechanism of the Qinghai-Tibet Railway effect？ And is there heterogeneity in the impact of the Qinghai-Tibet Railway on different regions？ To answer these questions， a difference-in-differences （DID） model is proposed basing on the quasi-natural experiment of the opening of the Qinghai-Tibet Railway. Using panel data from the Qinghai-Tibet region from 2003 to 2020， the effect and mechanism of the opening of Qinghai-Tibet Railway on the economic， social， and cultural development of the regions along the route are explored. Parallel trend test， random selection of treatment groups and instrumental variable method are used to verify the reliability of the research conclusions. The DID method can overcome biases in modelling estimation caused by variable endogeneity and omitted variables， making it an effective method for evaluating the externality on the opening of the Qinghai-Tibet Railway. Results show that the opening of the Qinghai-Tibet Railway generally increases the GDP per capita of the regions along the railway， reduces the income gap between urban and rural residents， and significantly increases the number of cultural enterprises and the total tourism income. Meanwhile， the effect of Qinghai-Tibet Railway is sustainable. Mechanism studies find that Qinghai-Tibet Railway promotes the economic， social and cultural development along the line by stimulating investment and developing service industry， promoting employment， increasing population mobility and attracting tourists. Heterogeneity analysis shows that the economic， social， and cultural effects of the Qinghai-Tibet Railway have a greater impact on non-central cities along the railway than on central cities. These findings suggest that the Qinghai-Tibet Railway is conducive to structural transformation and shared prosperity in the Qinghai-Tibet region， and its economic， social and cultural effects are continuous. This quantitative analysis framework for the externalities of mega-railway projects provides theoretical support for promoting the high-quality development of similar projects， as well as the sustainable and harmonious regional development.