Air entrainment is known to be one of efficient and inexpensive methods to prevent cavitation damages in hydropower projects. The shape of sudden expansion-fall is used as a common device for mitigating cavitation erosions. The complex flow patterns with cavitation are numerically simulated by using the realizable k-ε turbulence model and the air-water mixture model. The calculated results are compared well with the experimental results as well as those obtained with the k-ε turbulence model with the Volume Of Fluid (VOF) Model. The calculated results agree well with the experimental data for the aeration cavity and wall pressure. Moreover, the air concentration near sidewall is simulated by a mixture model. It is found that the mixture turbulence model is superior to the VOF turbulence model.