In order to investigate the application of Interior Permanent Magnet (IPM) machines in the aerospace high-speed starter generation system, a 250 kW, 25000 r/min high-speed permanent magnet starter generator for aircraft is designed. An analytical stress model of the interior permanent magnet rotor structure is established to analyze the structural strength and optimize the carbon fiber sleeve. The accuracy of the stress model is verified with help of the finite element analysis (FEA). The FEA is used to analyze the electromagnetic characteristics of the machine, and the efficiency of the starter generator fed by converter is analyzed by the field-circuit co-simulation. The rationality of the design scheme is verified, which would be helpful on the application of the interior permanent magnet motor in the aviation system.