Abstract: Refined oil pipeline operation will be threatened by corrosion products from the water at low spot which block the products pipeline.To study the mechanism of pipeline with water inside,the calculation formula of water phase thickness gradient is given according to the two-phase model that is applicable to oil-water two-phase coexistence in one pipe.The phase interfaces of water carried by oil in different inclination pipeline are all analyzed theoretically,and the experiment program can be guided by the analysis results.The temperature rise in experiment should be recorded to confirm the physical properties changes.Moreover.the variable range of inclination should be decreased when the inclination is small and vice versa.