Abstract: High density saltwater discharge occurs frequently and exhibits complex hydrodynamic characteristics during seawater desalination. To study the hydrodynamic characteristics of saltwater jet under wave action, a three-dimensional computational fluid dynamics mathematical model of negative buoyant jet with vertical round was developed under regular waves. The model was validated via comparison with the experimental data. The comparison indicated good agreement between the model and experimental data. The diffusion characteristics of negative buoyant jet, the three-dimensional time average velocity, and the instantaneous concentration characteristics were analyzed. The results indicated that the wave height and period contribute slightly to the decay index of the dimensionless average vertical velocity in the jet axis. However, they affect the decay coefficient. An increase in wave height or wave period leads to an increase in velocity half-width, the decay coefficient of dimensionless average vertical velocity on the jet axis decreases. Hence, it contributes to jet diffusion in ambient water. Additionally, the wave to jet momentum ratio is used to conduct the equations of the dimensionless average velocity decay coefficient and the half-width of mean characteristic velocity, which can provide some reference for practical engineering applications of the negative buoyant jet.