Abstract: Through dynamic river bed experiments and finesand river bed in lower Yellow River, localized scouring on piers underunsteady flow when river channel is narrowed in large scale is researched.The result indicates that the localized scouring on piers under unsteadyflood and scouring under steady flood are different and related necessarily.Through analysis of influencing factors and experiment data, their relationand relevant calculating methods of localized scouring depth on piers underunsteady flow are established. Compared with prototype observed data underunsteady flow flood, the result is reasonable and accords the practice well.