The gas flow pattern in the radial flow bed is simulated by porous and transport models combined with a 6-lump kinetic reaction model (C4 hydrocarbon catalytic pyrolysis), which are verified by the published experimental results. Aside from the simulation method, the gas axial dispersion behavior is well explained by introducing the "common pressure pool" (CPP) and the "constant pressure drop lines" (CPDL) methods. The most severe gas axial dispersion behavior occurs at the turning point of (r-r(1))/(r(2)-r(1)) = 0.62. However, the gas flow pattern can still be roughly seen as a plug flow in whole bed for the small influences of the gas axial dispersion behavior. The appropriate gas residence time can then be determined by the plug flow model and the simulation method to achieve different production targets.