Numerical analysis was carried out to investigate nitrogen absorption rate accompanied with Marangoni convection due to surface tension gradient on the free surface of liquid iron by using the commercial CFD software package. Good agreements between the experimental values and the calculated results were attained with various oxygen contents. It could be deduced that the Marangoni convection occurred continuously until the liquid iron is saturated with nitrogen, since the gradient of the nitrogen concentration could be maintained on the free surface of liquid iron owing to flow of the liquid iron. The decrease in nitrogen absorption rate with increasing oxygen content under non-inductive stirring condition could be attributed to the dwindling of convection in liquid iron and the effective diffusion coefficient as the liquid iron flow changes from the turbulent to the laminar flow.