The objective of present study is to predict the performance characteristics of the first stage compressor in a total 3-stage 5000 HP-level turbo compressor. CFD commercial code, CFX has been used to predict three-dimensional flow characteristics inside of the impeller, diffuser and volute. The impeller is made of 17 blades and the diffuser consists of 11 vanes. Shear Stress Transport (SST) model has been used to simulate turbulent flows through Reynolds-averaged Navier-Stokes (RANS) equations. Grid dependency has been also checked to get optimal grid distribution. Numerical results have been compared with the experimental test results to elucidate performance characteristics of the present compressor. In addition, flow characteristics of the impeller only have been studied for various blade configurations. Angular offset in leading edge of the blade has been selected for the optimal blade design. Performance characteristics in terms of efficiency and pressure ratio between the impeller entrance and exit have been investigated for the selection of optimal blade design. Also, flow instability such as surge phenomena has been studied and anti-surge characteristics have been checked for various blade configurations in the operational window.