Abstract: The collapsible loess has a large compressibility and a low strength. It often produces a larger settlement when the subgrade is built on it, and the rain often leads to subgrade subsidence and other subgrade diseases, which has seriously affected the construction of the railway. In order to prevent subgrade subsidence of loess, Hejin to Sanmenxia DK531+702.50～DK532+006.13 of one railway is taken as the test road section to study grain composition, physical-mechanical property and soluble salt composition analysis. It is concluded that the physical-mechanical property of the loess affccts the collapsible damage of loess roadbed deformation. Due to the high silt content in the loess, collapsibility may happen at a low moisture content; the subgrade subsidence of loess roadbed is mainly caused by tremendous variety of cohesion, while angle of internal friction has no distinct variety. Foundation treatment method and drainage measure are put forward combining with the engineering geological properties of the research section, which provides a basis for preventing and curing the subgrade diseases of loess roadbed.