Abstract: The formula for calculating the incipient motioncondition of non-uniform sediment has been established by consideringthe equivalent grain and the relative exposure degree. The results showthat the coefficient of the formula is not a constant butvaries in a range with the diameter, relative exposure degree and incipientstatus of grain. The formula for uniform sediment has also beenobtained, with the coefficient in a range. The domain of coefficient valuecalculated in the formula has been verified by using other coefficientdata. The results show that the equivalent grain can reflect thecharacteristics of the sediment incipient motion.