Abstract: Some dozens of conditions of incipient motion of sediment proposed by various investigators are transformed into a unified form in terms of dimensionless critical shear stress(or tractive stress) θ_c=τ_c/(γ_s-γ)d.The values of θ_c for non-cohesive sedinvents with uniform diameters are calculated,which generally lie between 0.0231 and 0.0716.The differences of various equations can be distinguished from the results calculated.Thus,a scientific basis can be provided for selecting and using the equations.