The low-head runoff type power stations are often non-regulating reservoirs.To control the flooded line in the reservoir area,during the flood period the hub is always run by pre-empting the storage capacity.Affected by the flood discharge and duration,the operation low water level of the hub has great changes during different periods,which makes the determination of the ship lock’s lowest navigable water level complicated.Taking the second-line shiplock project of Dayudayu navigation power hub in Xiangjiang River for example,adopting the synthetic diachronic curve method and instantaneous water level duration & times,and combining with actual navigation conditions of river sections,we determined ship the lock’s lowest navigation level.The method may serve as reference for the determination of the lowest navigable water level of ship locks.