(Abstract) This paper designs the rotor structure of a permanent magnet (PM) synchronous generator by a topology optimiza-tion method. The implemented optimization method is the Genetic algorithm coupling the concept of cluster of materials and a cleaning procedure, and then it assumes four hexahedron PMs similar to the rotor shapes obtained by the pro-posed method for reasons of manufacturing ease. This paper manufactures the optimized rotor structure, which has a high flux linkage. Experimental results clarify that the voltage regulation is improved and that the efficiency is improved.