The viscous flow in the CHON system liquid rocket engine nozzle was simulated using loosely coupled pointedimplicit MacCormack scheme. The reacting model and nonreacting model were used in the simulation, and a 12species, 14steps finiterate chemical reaction model was adopted in the CHON reacting model. The distributions of flow parameters in the nozzle were presented. Analysis of the results shows that the numerical simulation results are in accordance with the theoretical distributions of flow parameters in the nozzle. The numerical results provide reference for design and experiment of the rocket engine.