The helium tracer method is used to investigate the residence time distribution and flow patterns of feed spray in different fluid catalytic cracking feed injection schemes by cold model experiments. The axial Peclet number in the upward and downward oriented feed injection schemes was obtained by fitting the residence time distribution into the one-dimensional axial dispersion model with an open open boundary condition. Results suggest that the flow pattern of the mixed stream is closer to complete mixing in the initial contact region of spray with catalysts when the nozzles are mounted downward. A flow pattern variation index beta is proposed to show the flow patterns in the feed injection schemes quantitatively. It is shown that a larger beta is obtained when the feed nozzles are faced downward, meaning that the flow pattern of mixed stream in the feeding zone can develop more, quickly from a likely complete mixed flow into a likely plug flow.