Abstarct: Permanent Magnet (PM) machines are large-scale used, remarkably in the past couple of decades. Two substantial considerations are highlighted correlate to PM machines that are cost competition and availability of rare-earth PMs. High-power density, low manufacturing costs, which are a consequence of the overall weight and the size reduction, are the advantages of the aforementioned machines. High-Speed Permanent Magnet Synchronous Generators (HS-PMSGs) are utilized in commercial, industrial and, even home applications. One challenge is that they suffer from the mechanical stresses of the rotor as one of the significant problems. So, the design procedure of HS-PMSG faces numerous challenges and hindrances. One of the recommended methods is utilizing the retention sleeve. The importance of the retention sleeve becomes conspicuous when the rotor encounters the radial and tangential stresses derived from the high speeds. Nevertheless, choosing the optimal thickness for the retention sleeve as well as a PMs which provides both the proper mechanical and electromagnetic operation conditions for the HS-PMSG, is an issue. In this thesis, a novel method to finding the appropriate dimensions of the retention sleeve and PMs baxsed on the well-known Taguchi optimization method has been presented. A 60-krpm, 2-poles, 18-slot HS-PMSG analytically designed at the first step, and next, it has been optimized by Taguchi optimization method, and finally simulated and modeled through FEM analysis using JMAG 17.1 and ABAQUS CAE. Results obtained from the electromagnetic and mechanical simulations of HS-PMSG shows that in the optimized design of HS-PMSG; • The effective air gap has been reduced which leads to the better electromagnetic and mechanical performance of HS-PMSG compared to the initial design. • Owing to the reduction in the thicknesses of the retention sleeve and PM, it can be concluded that the total size and dimensions of the HS-PMSG have been reduced. • The weight of PM and the retention sleeve are reduced by about 16.31% and 29.28% responsively, and as a result, the total weight of HS-PMSG is reduced approximately 1.94%, • The Joule loss is reduced by about 9.80%, • The HS-PMSG efficiency has been improved by 0.02%, • And finally, the cogging torque is reduced by 27.87%, comparing with the initially designed machine.