A numerical study on a suction vortices, free vortices and subsurface vortices behavior in the model sump system with multi-intakes is performed. Especially a numerical analysis of very complicated three dimensional multiphase flows through the model sump is done by using the finite volume method of the CFX code with multi-block structured grid systems. A k-ω Shear Stress Transport turbulence model and the barotrophic cavitation model are used for solving turbulence cavitating flow. From the numerical analysis, several types of vortices are investigated and their formation, growing, shedding and detailed vortex structures are studied. To reduce abnormal vortices, an anti-vortex device is considered and its effect is estimated and discussed.