The generation of orthogonal grids is the basic and key ingredient of computational dynamic fluid.Based on the numerical and physical properties of stream and potential functions,an algorithm to get orthogonal grids is proposed in terms of numerical solutions of above functions by the finite element method.The numerical result shows that the present method can guarantee the orthogonality of the generated grids.Moreover,the resulting grid space is easy to adjust,so the method is especially suitable for grid generation in complex geometrical regions.