This paper presents design and comparative study of high torque coaxial permanent magnet couplings (CPMC) for the use in a tidal current generation (TCG) system. Two different models such as a radial flux-CPMC (RF-CPMC) with magnet retaining rings and a flux concentrating-CPMC (FC-CPMC) with inner and outer rotor yoke changed by retaining rings are analyzed to find the best model under certain design constraint conditions to achieve a minimum pull-out torque of 1.0 kNm. Moreover, the effect of the electromechanical characteristics such as the radial force, stress and deformation are analyzed for both models. Based on the analysis it is found that both RF-CPMC and FC-CPMC are capable of producing the pull-out torque higher than 1.0 kNm, however considering the installation environment and the magnet use, RF-CPMC is selected for prototyping, which is tested using a 3 MW induction motor based dynamometer system to compare its torque production capability with respect to the simulated model. The comparison shows that the prototype is capable of producing the required amount of pull-out torque.