The most common devices used for extracting the ocean current energy are the current turbines. Most people use the wind turbine blade design methods for the horizontal axis current turbine design; however, the current turbines operate in the water, and their physical behaviours are more like marine propellers. In this paper, two turbine blade design procedures are adopted. The first design procedure is similar to the propeller designs, and the second design procedure is to use Genetic Algorithm and boundary element method (BEM) to find a geometry which can provide the maximum torque. After completing the designs, hydrodynamic performances of the marine current turbine are then computed and analysed by the potential flow BEM and the viscous flow RANS method. The computational results show the geometries designed by the presented procedures can not only satisfy the hydrodynamic design goal, but also predict the delivered power very close to the experimental data. After the blade performance meets the design target, the performances of designed 20kw floating type Kuroshio turbine including the floating body at different operation conditions are demonstrated in the paper. Also, the structural strength of the turbine blade is computed by FEM, and the results are evaluated to see if the design complies the rule requirements.