Abstract: The shortage of the current standards for estimating the incipient ration of sediment particles is analyzed in this paper. The standards for estimating incipient ration of sediment not only should consider the condition of river flow,but also consider the relative location of sediment grains within riverbed. The condition of incipient rmtion for one diameter grain is not a constant,but a variant located in a region and varying with the relative expose degree of the grain. The formula for calculating the conditions of threshold rmtion is obtained according rolling ride based on force and momentum balances,and the value of dimensionless critical shear stress of each status is calculated theoretically.