A precisely quantitative description of critical hydrodynamic characteristics of soil detachments was a important for developing physically based soil erosion model. In this study, the critical hydrodynamic characteristics of soil detachment on yellow soil slope were measured under different antecedent soil moisture contents（5%～23%）and slope gradients (1°～10°), the impacts of soil moisture content (3%～23%) on shear strength were also investigated. The study comprehensively analyzed the effects of different antecedent soil moisture contents, slope gradients and soil shear strengths on critical hydrodynamic characteristics. And the results showed that critical flow rate had power function relationship with slope gradient and antecedent soil moisture content. In this paper, an accurate equation was proposed, which reflected combined effect between the antecedent soil moisture content and slope gradient on critical hydraulic characteristics. A simplified power function could be used when the slope gradient was smaller than 5°. This equation could ignore the impact of the antecedent soil moisture content. Soil cohesion reached peak firstly and then fell down to stable with the increase of the antecedent soil moisture content. While the critical hydrodynamic characteristics of soil detachment showed a gradually decreasing trend.