A modified k-epsilon two-equation turbulence model was developed to improve the consideration of the important buoyancy effect on turbulence and turbulent transport. which is a serious deficiency of the standard buoyancy-modified k-epsilon model. The present model was tested against both plane and axisymmetric thermal plumes and a buoyant diffusion flame. The model was found to be stable, computationally economic, promising and applicable to complex situations. The predicted plume spreading rates and velocity and temperature profiles agreed well with experimental measurements. When compared with the standard buoyancy-modified k-epsilon turbulence model, this model gives significantly improved numerical results.