The center body diffuser is one of supersonic diffuser that can simulate high-altitude environment. There is center-body structure inside the diffuser, and a complex fluid flow is occurred inside the diffuser because of the interaction of the CB structure with gas exhausted from the nozzle outlet. In this study, starting point and flow characteristics of diffuser were investigated according to changing the CB nose cone angle and the length of distance between nozzle and CB structure. The differences of the supersonic flow were compared through each parameter of CB distance and CB nose angle. First changed parameter was length between nozzle and CB. According to the length of distance between nozzle and CB, axial momentum was developed and oblique shock wave moved front of CB from end of CB nose cone. Also, when CB position was located on a certain length, starting point of CBD decreased. Next change parameter was angle of CB nose cone. According to the angle raised, angle of oblique shock wave was raised and radial momentum of supersonic diffuser developed. But, according to radial momentum of supersonic flow over certain angle, the starting pressure of CBD increased. Because axial momentum which isolated vacuum chamber from atmospheric pressure. Through these CFD analysis results, it was shown that angle and length of distance between nozzle and CB influent performance of CBD.