In this study, the radial flow turbine of a cooling turbine is investigated numerically and then compared with the experimental results at some operation conditions. Performance characteristics of the compressor are obtained experimentally by measurements of rotor speed and flow parameters. In this investigation, the turbine performance curve is obtained and three dimensional flow field in the turbine is analyzed. The rotor and casting geometry are modeled in BLADE GEN and CATIA softwares respectively. The TURBO GRID software is used for grid generation of rotor while the ANSYS MESH software is applied for grid generation of casting. Finally, 3D numerical solution of fluid flow in the turbine is solved by CFX flow solver. In this approach, compressible flow equations are solved according to the pressure based method with SST turbulence model. To ensure the numerical results, the grid independency is studied. Finally, the performance characteristics of the turbine are obtained numerically which are then compared to the experimental results. The comparison shows good agreement between numerical and experimental results.