To improve the description ability and reliability of the workflow management system used in large enterprises, this paper proposes a flexible workflow model based on the N-version programming. Compared with the traditional workflow model, the model applies the N-version programming method on the key node in the workflow to significantly enhance the reliability of the workflow management system. Furthermore, how to maximize the reliability of the N-version programming method is described to meet the practical needs of the model application. Finally, this paper introduces the realized workflow model and the corresponding system in detail. The experiment result shows that the new modeling method is high efficient and satisfactory.