Abstract: Three-phase medium of oil-gas-water has different physical and chemical properties, the mixture from it produces a mixing interface with uncertain phase states and distribution in time and space. This paper studies the oil-gas-water three phase blending process within pipe by means of VOF model and identifies its flow pattern. The impact of initial GVF on flow pattern is researched and the bubble flow and plug flow, common in engineering practice, are found, and further, the impact of flow velocity on bubbles in bubble flow is analyzes. The results show that as for bubble flow, the distribution of bubbles has direct relation with liquid velocity, the lower the flow velocity is, the more uneven the distribution of bubbles is. Simulation results are well fitted with related results, which can provide a certain theoretical guidance to engineering practice.