Abstract: The flow and dilution of a vertical round jet under the combined effect of wave and current are investigated by using the three dimensional large eddy simulation model, and the wave effect on the 3-D concentration characteristics of the jet is discussed. The comparison between the numerical results and the experimental data shows that, the numerical model is capable of reproducing the distribution of the jet velocity and concentration along the water depth in the wave-current environment. The 3-D concentration characteristic indexes of jet, including the minimum dilution and its vertical position as well as the visual area of the section, are adopted in this study. It is found that, the jet in a wave-current environment shows a larger visual area on the sections as the increasing of the wave height or period, which indicates that the wave has a positive role on the acceleration of jet dilution in the wave-current environment.