Based on CFD method, porosity and resistance coefficient was introduced to develop a mathematical model for radial-flow fixed-bed reactor (RFBR). The commercial CFD code FLUENT6.1 was applied to simulate the flow field in four kinds RFBRs with different flow modes. Some detailed information about the velocity and pressure distribution in these reactors was obtained. The simulated results show that most gases passed through the catalyst bed along the radial direction with the effect of bed resistance. The velocity distribution in the middle of the catalyst bed is approximatively uniform. The flow in outward RFBR is better than that in inward RFBR, and the flow in outward Π-shaped RFBR is better than that in outward Z-shaped RFBR. The axial non-uniformity in inward Z-shaped RFBR is maximum, then followed by inward Π-shaped RFBR, outward Z-shaped RFBR, and outward Π-shaped RFBR. The flow in outward Z-shaped RFBR is the most uniform.