In order to understand the difference of ventilated supercavity in water tunnel and infinite flow field,3-D numerical simulations are carried out to obtain the ventilated supercavity in above mentioned conditions based on RANS equations,using the finite volume method and SST turbulence model in the framework of the two fluid multiphase flow model.The numerical method adopted in this article for the infinite flow field and water tunnel experiments is validated by comparing results with those of empirical formulas and experimental data.On this basis the difference between water tunnel experiments and infinite flow field is studied,including the influence of the route loss and the blocking effect in the water tunnel.Finally,some suggestions are made for water tunnel experiments.