Permanent magnet motors have some advantages such as high power density, high efficiency and good thermal characteristic and are used in many industrial applications. The aim of this paper is to present the optimal design and fabrication of a counter rotate brushless permanent magnet motor for using In under water systems. Due to the motor space limitations and lack of heat transmission with the environment, the designed motor must have high power density meanwhile high efficiency. For this purpose, the motor dimensions are calculated with goal of increasing power density and efficiency by using motor’s electromagnetic equation and genetic algorithm. In order to validate the calculated results, the motor has been simulated with finite element method. At the end, the motor has been fabricated according to the calculated parameters and the experiments results have been presented.