In order to comply with recent legislations against exhaust gas emission and vehicle fuel consumption, demands on improvement of turbocharger performance are increasing. The demands of compressor performance for a wider range and higher efficiency are especially strong, while the control of complicated inner flow is important to improve such performance. At the same time, the growth of computing capacity has made a large-scale computing possible, not only in academic study but also in commercial development. The improved computational fluid dynamics method combined with the experimental fluid dynamics made it possible to understand and control unsteady and asymmetric aerodynamic phenomena that can be applied on the improvement of compressor performance. This paper describes an example of performance improvement activity in controlling "tip leakage vortex," which has strong unsteady and asymmetric characteristics.