This study tris to reveal the relationship between DEM terrain attributes and flow accumulation threshold (FAT) used to extracted gullies in a severe soil erosion region (SSER) of the Loess Plateau of China based on PCA, which will help to pick out the main influence factors in the initiation and development process of Loess gullies. The study region consists of 22 typical watersheds. A series of gully densities produced by different FAT was obtained, and mean change-point was used to identity a best threshold in every watershed. After terrain attributes were calculated based on ArcGIS, a PCA method was used to study the relationship between terrain attributes and FAT. The results show that the FAT increases from north to south, or from east to west in the SSER of Loess Plateau across the entire study area, consistent with the geomorphological types of Loess Plateau. The effective composition of the terrain Factorscan be separated into three groups, namely slope group, relief group, and thw elevation variation group. The maximum value in slope group shows a positive correlation with FAT, and the order can be described as gradient > roughness> terrain curvature> plan curvature > profile curvature. The average value of the relief group also shows a positive correlation to FAT, and the order as relief degree of terrain > dissection index of terrain, while elevation variation group has a negative correlation with FAT. The contribution rates of principal components are 58.754%, 18.915%, 11.388% respectively with weights of 0.527, 0.229, -0.569. The research implies that the slope characteristics are important factors affecting the development of loess gullies.