The multiphase Halbach array permanent-magnet machines are very good candidates for special applications such as marine and military applications due to the fault tolerance capability, high output torque, and high acceleration features. In this paper, an optimal design of a five-phase Halbach permanent-magnet machine for high efficiency, high torque, and high acceleration is investigated. A Genetic Algorithm method is used to optimize the design variables based on the analytical model of the motor, which is dependent only on motor geometrical and materials data. In this method, first the main machine design objectives such as efficiency, acceleration, and output power are optimized separately and then a multiobjective optimization considering all objectives simultaneously is given. The detailed finite-element analysis results are carried out to evaluate and verify the performance of the designed machine.