A comprehensive three-dimensional (3D) heterogeneous reactor model based on the Eulerian-Eulerian approach was applied to simulate the turbulent gas solid flow and catalytic cracking reactions in a fluid catalytic cracking (FCC) riser reactor. In addition, the 14-lump reaction kinetic equations were incorporated into the reactor model to describe the FCC reactions. First, the model at cold- or hot-model conditions was verified by comparing against the open experimental data. Second, the effect of the nozzle jet velocity on the flow of the feedstock injection zone of the riser was investigated numerically using the model at the cold-model condition. Finally, the influences of nozzle position and angle in the riser on the performance in the feedstock injection zone under the reactive conditions were investigated numerically. The simulation results showed that the nozzle jet velocity plays an important role in determining the two-phase flow in the feedstock mixing zone while the nozzle position had a small influence on the flow field and the cracking reactions in the feedstock mixing zone. It also showed that the nozzle angle had a significant influence on both the flow field and the cracking reactions in the feedstock mixing zone. The reactor with a nozzle angle of larger than 30 degrees was preferable.