In order to analyze the shipping influence caused by Xiaonanhai Hydropower Station,in the article, the Saint-Venant partial differential equations are used together with Preissmann implicit difference for building a one-dimensional unsteady flow hydrodynamics model and the model was verified with the observed hydrological data. By simulating hydrodynamics for the daily regulation, the capacity of navigation in the lower reach are estimated. The simulating results show that the situation might deteriorate the flow condition in downstream in the case of daily regulation whose operating rules were formulating from the side of load, thereby impair the navigation during the low-flow phase. It is necessary to adjust the operating rules of power station or implement river regulation works for the lower reach after dam.