Abstract: Since traditional methods to measure bed shear stress fail to world in the presence of seepage,alternative approaches to study the response mechanism of bed shear stress to seepage are limited to some theatrical analyses with some assumptions and indirect estimation.The issues of whether seepage reduces or enhances bed shear stress are still matters of considerable debate.To this end,a special-designed device is deployed to directly measure the bed shear stress in the open channel flume with varying seepage rates.Experimental results show a close relationship between changer in bed shear stresses and the relative seepage intensity v_s/U.Variation in bed shear stresses with seepage has an inflexion and a critical value when the |v_s/U| is about 0.2% and between 0.2% and 0.4%,respectively.Therefore,it is clear that the range of v_s/U investigated experimentally is the leading cause of the contradiction in the literatore.