Influence of slag viscosity and composition on the inclusion content in the steel is studied using laboratory experiments and modeling simulations. The steel samples are taken during the experimental process to record the inclusion content change. Afterwards the prepared samples are analyzed using automated scanning electron microscope and energy dispersive spectroscopy (SEM/EDS) method. A simple steel/slag reaction model is constructed based on the effective equilibrium reaction zone (EERZ) method. The inclusion content evolution process is discussed by combining the experimental and calculated results. It is found that the inclusion content evolution in the steel is determined by the inclusion generation and removal.