Abstract: To address the mixing problem of materials inside the first reactor of a polypropylene unit, this study applies computational fluid dynamics (CFD) to analyze the internal flow field of the reactor. First, CFD software FLUENT is used to simulate and compare the effects of a pitched-blade open turbine impeller and a pitched-blade disc turbine impeller on the flow field distribution within the stirred tank. Then, a three-dimensional simulation of the stirring process is carried out using the standard k–ε turbulence model.The simulation results indicate that the pitched-blade disc turbine impeller produces more sufficient flow circulation within the reactor and achieves better mixing performance. Subsequently, different impeller spacings of the first three rows of pitched-blade disc turbine impellers are simulated. The results show that when the impeller spacing is D = 1.0D₀ (where D₀ is the impeller diameter), the mixing effect is optimal. Finally, the flow field distribution under different blade inclination angles is analyzed, and the optimal blade tilt angle is determined. After modifying the impeller structure based on the simulation results, the reactor product quality fully met the required standards.