Abstract: The study on flow patterns and patterns transition in recent years is summarized. Flow patterns in vertical, inclined and horizontal pipe are introduced. The effect of inclination angles on the region of flowing patterns is presented. The flow patterns with different inclination angles are compared. Since gravitation and inclination angles, the flow patterns in inclined pipes are different from those in vertical pipes. Oil water two-phase flow is classified into tow categories, segregated flow and dispersed flow. The transitions criterion in segregated flow and dispersed flow, influent factor of transition and the effect of inclination angle on transition criterion are introduced, transition criterions are also compared. These transition criterions are completed in horizontal or vertical pipes. Criterion in inclined pipes need to be studied further, it is one of the research direction in oil-water flow for the further.