Abstract: Debris flow is a typical rainfall-induced geological hazard in the Loess Mountainous Areas, posing a serious threat to the safe operation of railways. This study selects representative debris flow gullies along the railway in the northwestern loess mountainous areas as research objects to further improve the understanding of debris flow characteristics and risk assessment methods for railways in the Loess Mountainous regions. Based on data collection, remote sensing investigation, and field investigation, dynamic parameters of debris flows were calculated, flood discharge capacity of existing culverts was checked, and numerical simulations of dynamics processes were carried out to identify the impacts of debris flows on railways and surrounding areas, and a debris flow risk assessment method was proposed. The steep topography and abundant loose materials in the study area provide basic conditions for debris flow initiation. Two formation modes are identified: rainfall-induced slope erosion type and collapse-landslide type. For rainfall-slope erosion debris flows, the single-event outburst volume calculated by the rain-flood method can be discharged through the culvert, posing little threat to the open-cut tunnel and surrounding environment. Under heavy rainfall, if spoil at the gully head and steep bank collapse simultaneously to form collapse-type debris flows, the disaster scale will increase significantly. Numerical simulation results indicate that after initiation, debris flow will deposit in front of the open-cut tunnel, overtop the structure, and threaten residential areas below the railway. Based on debris flow susceptibility and the inhibition effect of existing bridges and culverts on debris flow hazards, this paper proposes a debris flow risk assessment method suitable for railways in the Loess Mountainous Areas. The results can provide new insights and technical references for the prevention and risk investigation of railway debris flow disasters in loess mountain areas. Future research should further consider the dynamic impact of debris flow impact loads on railway structures to refine the precision of debris flow risk assessment systems.