Abstract: Three-dimensional CFD technology was used to simulate the flow field of COIL mixing nozzle. Concentration-driven as well as pressure-driven diffusion terms were considered in the diffusion equations. The 10 species and 21 reactions chemical model was applied to implement the chemical kinetics. Some elementary fluid dynamic phenomena of a round transverse jet were obtained such as the horse-shoe-shaped jet trajectory and the counter-rotating vortex pairs. The results indicate that the pressure-driven diffusion term has contrary effects on species of different molar weight, the molecular of "heavier" species diffuses toward the pressure gradients and that of "lighter" species against the pressure gradients. It was also found that even complete jet penetration was not achieved, the gain field