Compressor plays a crucial role in the air management system (AMS), which is used in fuel cell systems (FCS). In this paper, an impeller of centrifugal compressor for AMS of a 65 kW FCS was designed. The performance of initial designed impeller was investigated by computational fluid dynamics (CFD). The univariate parameters of initial impeller were analyzed. The simulation results show that the geometric parameters of the impeller inlet section, blades and outlet section have a great influence on its performance. According to the simulation results and theoretical analysis, the impeller was optimal designed. The optimal designed impeller has higher pressure ratio and efficiency. The impeller has relatively flat operating characteristics not only at the design condition but also at other operation conditions. These could meet the requirements.