In order to provide scientific basis for soil and water conservation measurements of the loess plateau, overland flow with a hydraulic flume with adjustable bed gradients was used to study the seasonal changes in soil detachment capacity and the potential influential factors during one growing season of maize and millet in 2012. The results showed that the soil detachment capacity for each fibrous crop fluctuated significantly over time with a similar pattern of seasonal change. The seasonal changes of soil detachment capacity were affected by tillage practices, soil consolidation, water-stable aggregates, and root growth. Soil detachment capacities of two fibrous crops could be estimated by using flow shear stress, soil cohesion and root density (R²＞0.75, NSE＞0.74).