The experimental investigation on flow pattern and its transition for gas/oil-water emulsions in vertical upward pipe has been undertaken. In the test series the input water fraction in oil-water emulsion was varied between 0% (pure oil) and 100% (pure water). The test section was a steel tube with inner diameter of 44mm and length of 1.5m. The pressure conditions for test section were varied between 0.1 MPa and 0.5 MPa, the temperatures were varied from 10 to 40 °C, gas superficial velocity VSG = 0.1 ∼26m/s, oil-water emulsion superficial velocity VSL = 0&SIM;2.5m/s. The test oil was 46# machine tool oil. In this paper, the flow pattern characteristics of bubble and slug regime at w/o (water in oil) and o/w (oil in water) are described. The phase inversion point between w/o and o/w is obtained through used the Yeh method and the pressure drop of test section. The water fraction at the phase inversion point is 0.56. There are certain relations between flow patterns, frequency and amplitude of pressure drop pulsation. In the experiments a group of data which determine flow pattern by pressure drop pulsation has been obtained for vertical upward pipes. The predictable model for flow pattern transition is established. The predictable model is in good agreement with experimental results.