Taking the vertical densitystratified ambient fluid into consideration, a vertical twodimensional model for buoyant jet was established based on a kε turbulent model. Finite volume method and SIMPLE algorithm were used to obtain the solution of the model. Numerical simulation of vertical buoyant jet in linearly densitystratified ambient fluid was simulated, and the distribution of density, trajectory, dilution and width of the jet were obtained. The numerical simulation results were in good agreement with the experimental results, which means that the vertical twodimensional buoyant jet model can exactly simulate the behavior of buoyant jet and the mixture of the buoyant jet and ambient fluid.