Analysis of air bubbles entrainment in liquid slug body is one of the most important and complicated phenomena during slug flow regime. In the present attempt, a method is proposed for slug modeling to consider the air bubble entrainment into slug liquid body. The effect of consequencies and their impact on slug behaviour to predict more accurate correlations for slug parameters are estimated and calculated. This method considers a two-fluid single pressure model, combined with population balance model for equal bubble diameter series and solves using volume of fluid. In this regard based on slug and hydraulic jump similarity, a correlation for air bubble entrainment rate and its mechanism selected. This correlation developed in the form of a user defined function code and coupled with other models in FLUENT solver to calculate slug flow. Finally the result of this numerical modeling is validated with the result of other numerical and experimental results where exist in the related literature. The result is consist of the slug flow profile, entrained air bubble profile and their diameter distribution, vortex at slug front, pressure distribution during slugging, slug mixture velocity, turbullent model parameters and etc.