The 'Cluster Fan Engine' was designed for personal aircrafts and VTOL aircrafts, having many merits including reliability of operation, flexibility of mounting, maintainability, extremely low development costs and initial costs, and wide variety of potential applications. Because new concepts were applied to aerodynamic components of the engine to reduce number of parts for itself, it is difficult to design the component based on the existing experimental data. Therefore, numerical simulations are conducted to validate the design process for the aerodynamic components. This report describes the design process of the mixed flow compressor based on the results of the numerical simulations.