Abstract: The Qinghai-Tibet Railway, completed on 1th July, 2006, greatly contributes to the development and understanding of the Tibet, deeply influences on China and others world, and has historic significance, social effect, politics sense and economic meaning for Chinese modernization construction and the development of the Midwest regional. Many factors affect railway trend scheme, and the most important factor is engineering geology condition on all the railway lines. By comparing with Qinghai-Tibet project, Gansu-Tibet project, Sichuan-Tibet project and Yunnan-Tibet project, it is believed to adopt Qinghai-Tibet project. Qinghai-Tibet Railway,the highest railway above sea level, was confronted with three main difficult problems: permafrost,high-cold and oxygen deficit and ecologic frangibility. Permafrost is the key problem, and it decides whether the Qinghai-Tibet Railway can successfully construct and whether its quality is high. Several generations exerting the most efforts, the Qinghai-Tibet Railway is all right open to traffic. Through retrospecting siting process and construction course, the author realizes hardship of constructing the Qinghai-Tibet Railway and importance of engineering geology.