Spiral separator has the characteristics of simple structure, light weight and wellseparated effect, which becomes one of the commonest centrifugal separator currently. CFD method was used to simulate wateroil separation in spiral pipe under the condition of a variety of entrance velocities and cross section shapes, and obtained a wateroil separation result that for a spiral pipe with circular cross section shape, the separation effect became sharper as the velocity increased, and too fast or too slow velocity both impacted the effect. When they were equal cross section areas, circular had a better effect than laddershaped and square cross sections. Based on the numerical simulation, the result provided a certain theoretical basis for spiral pipe technology.