Abstract: This paper presents a model for pressure-drop calculation of oil-water two-phase variable mass stratified flow in horizontal pipelines. The influence of inflow through perforation channels was taken into consideration and the model of oil-water variable mass stratified flow in horizontal pipelines was established by infinitesimal analysis. The mass and momentum conservation equations were established for oil and water phase respectively in the model, where the influence of wall inflow on pressure drop was considered. The basic model and pressure drop calculation model were established for oil-water two-phase variable mass stratified flow in horizontal pipelines. The influence of the following factors, such as inflow through perforation channels, the diameter of pipeline, and the viscosity of oil and water, on the pressure-drop in horizontal pipeline was simulated. The calculation result shows that pressure-drop along pipeline decreases with the increases of water cut when the viscosity of oil is higher than water and pressure-drop increases with the increases of water cut when the viscosity of oil is lower on the condition of exiting inflow.