By composing related equations and a new iterative method,the pervious segment wave algorithm of unsteady flow in open channel was improved.This method has high precision and very fast operation speed.The transient process of fluctuating wave in dynamic channel of Jinshuijie hydropower station was numerically investigated using this method when it unloaded completely,and a comparison with its original design data was made.The results manifest that the new method is correct and practicable.