The feedstock injection zone is a key section for Fluid Catalytic Cracking riser reactor. A 3-D Computational Fluid Dynamics simulation is performed by coupling the two-fluid model and the energy-minimization multi-scale (EMMS) drag. The prediction agrees well with the available data and the secondary flow phenomenon is captured. The simulation reveals that the M-shape distributed feed sprays interact with the W-shape distributed solid particles and then cause the undesirable W-shape distribution of the matching ratio of catalysts to feed. The transformation of such uneven distribution to the finally core-annular distribution heavily depends on the secondary flow, whereas its mechanism can be explained by using the Kutta-joukowski lift theorem. The increase of the feed spray velocity facilitates the feed diffusion and reduces the transition region. However, excessively high jet velocity may intensify the back-mixing near the wall and causes intense attrition or breakage of catalysts and thereby an increase of costs. (C) 2015 Elsevier B.V. All rights reserved.