The entrainment of the ambient air into a turbulent argon plasma jet is studied numerically using a turbulence-enhanced combined-diffusion-coefficient method. Namely, the Navier-Stokes equations and two-equation turbulence model coupled with the turbulence-enhanced combined-diffusion-coefficient approach are employed to predict the turbulent plasma jet characteristies including the evolution of air mole fraction along the plasma jet in air surroundings. Although complicated gas species always exist in the plasma jet due to rather high gas temperatures being involved, it is shown that the entrainment of ambient air into the turbulent argon plasma jet can still be treated simply by the combined turbulent and molecular diffusion between only two different gases (argon and air). Good agreement between the predicted results with corresponding experimental data reported by Fincke et al. [Int. J. Heat Mass Transfer 46 (22) (2003) 4201] demonstrates the applicability of the present modeling approach. (C) 2004 Elsevier Ltd. All rights reserved.