This paper applied the computational fluid dynamics (CFD) software to simulate 3-Dimensional flow field for a straight pipe stirred reactor. Multiple reference frames (MRF) impeller rotation model and standard κ-ε turbulence model were used to simulate the flow field by using Gambit to build 3-Dimensional reality model. Than it used Tecplot to treat calculation result. The result showed that the calculation model could simulate detailed information on distribution of velocity and turbulence kinetic energy. The maximum velocity and turbulent kinetic energy in the ractor distribute in the vicinity of blade tip.The overall flow trend of fluid is mainly ring circulation,which is conducive to the uniform mixture of materials in different areas; compared to single blade reactor, the combination of multi blade reactor can provide a turbulent flow of wider range. Under the circumstance of simulation material being water, the best speed corresponding to the reactor is 40 r/min.The paper proposed a application method of the reactor in water environment.