Abstract: The influence of feed injection velocity and angle on flow and reaction in a RFCC riser reactor was examined by using the three - dimensional differential numerical simulation method. The results showed that injecting velocity had a little influence on the form of flow field, but had influence on the distribution of catalyst and gas - phase concentration. The variation of injecting angle(with the axis of the riser) had a relatively greater influence on both flow field and reaction results. For the scope of the said research, the existence of an optimum injecting velocity and angle in riser could be established. The optimum injecting velocity was 60 m · s-1 of the angle 45°, and the optimum injecting angle should be no more than 45°.