Abstract: Bellow is key component of a supercritical gas centrifuge, which has changed the construction of the rotor’s wall and impacted the flow field inside the rotor. In order to analyze the impact of the bellow on the flow field in a gas centrifuge, numerical simulations have been carried out for flow fields with an inner bellow and an outer bellow respectively. The simulations of the flow field are based on the uni-connected hydraulic model and the Iguassu centrifuge model, and 2-D N-S equations are criticized and solved on the staggered grid by a homotopic method and the Newton iteration method. The simulation results show that the outer bellow has almost no effect on circulation flow, but allowable radial height of the outer bellow is very small in order to avoid the possible condensation of the UF₆ gas when keeping the waste withdrawal pressure constant. In addition, the inner bellow blocks circulation flow and results in the decrease of the separative power. According to the pareto analysis, the radial height of the inner bellow is the major impacting factor. Another result shows that, when the waste withdrawal pressure is constant, the radial height of the inner bellow is larger, the cut and the separative power is lower. In conclusion, during the design process of a supercritical gas centrifuge with inner bellows, it is necessary to properly design the radial height of the inner bellow to both lower the loss of separative power and ensure an achievable proper cut under safe working conditions.