为分析山区高速长大下坡路段事故严重程度的影响因素，首先对地处陕西省、广西壮族自治区、云南省的典型山区高速公路长大下坡路段的道路交通事故数据进行深度调研，共获取2559条事故数据，然后基于上述事故数据，构建了多项Logit事故严重程度模型，对导致山区高速长大下坡路段交通事故的直接致因进行了分析。分析结果表明：肇事驾驶人超速行驶、违法装载超限、疲劳驾驶、操作不当、违法停车、车辆制动失效对山区高速长大下坡路段伤亡事故有显著影响。研究结果为改善山区公路的运营安全性，从根本上寻求已建成山区高速公路事故频发的有效办法提供了方向。

In order to examine the significant factors of severity in the long and steep downgrade of mountain expressway, firstly, in-depth research was conducted on road traffic accident data of typical mountainous expressway long downhill sections located in Shaanxi Province, the Guangxi Zhuang Autonomous Region and Yunnan Province. A total of 2 559 accident data were obtained. Based on the above accident data, multiple Logit accident severity models were constructed to analyze the direct causes of traffic accidents on mountainous expressway long downhill sections. The analysis results show that speeding, illegal loading exceeding the limit, fatigue driving, improper operation, illegal parking, and vehicle braking failure of the driver in the accident have a significant impact on casualties on long and downhill sections of mountainous highways. The research results provide direction for improving the operational safety of mountainous highways and fundamentally seeking effective ways to prevent frequent accidents on built mountainous highways.