Abstract: A two-dimensional mathematical model of velocity field in a dredged channel at oblique angle to flow directin in open water is established in this paper. The calculated results are consistent with the experiment results by Yuan Meiqi, Li Anzhong etc.The velocity fields of natural condition (e. g. every kind of depth depth ratio, and angle between a degreded channel and flow direction) are calculated by this model.The figure of the coefficient of velocity ratio versus oblique angale with depth ratio (fig. 4) and the figure of flow direction in the middle of the gredged channel with dredged channel versus oblique angle with depth ratio (fig. 5) are obtained. Therefore, a basis is provided for selecting a proper direction for a dredged channel.