During the process of oil production and transportation, oil-water two-phase flow is a common occurrence. Well completion optimization and production design are greatly affected by the prediction accuracy of two-phase flow characteristics. In this paper, a novel model was proposed to predict the influence of interface shape on stratified flow. Dynamic contact angle theory and minimum energy method were introduced to solve the momentum equations with a curved interface and dispersed phase holdup in the lower water layer or the upper oil layer, respectively. If the interface shape changes from a flat surface to a curved surface, the flow area of the upper water layer will increase, and the flow area of the lower oil layer will decrease. Results showed that the dynamic contact angle and pressure gradient are greatly affected by oil superficial velocity, oil viscosity, and pipe diameter. By comparing the prediction with available experiment results, the validity of the model was evaluated. Results showed that the novel model had an overall good prediction performance for the dimensionless height of the oil-water interface at the mid-plane, the dimensionless height of water climbing, and the pressure gradient, with an average percentage error of 8.32%,16.09%, and 13.12%, respectively. The novel model is a unified model that could be used to solve the problem with a curved/flat interface. It will also promote the oil well production design and horizontal well completion optimization.