The relatively constant flow of the ocean currents carries large amounts of energy that can be captured and converted to a usable form. In this paper, design and performance simulation of a horizontal axial ocean current turbine (OCT) are studied. Also, study on varying the turbine duct housing design parameters and a series of simulation analyses were performed. Our model simulations with and without the turbine duct housing design were compared with existing literature results and very good agreements were obtained. The results also showed that unducted ocean current turbine power output is proportional to the cube of the current speed. Therefore, if we can increase the flow rate, the ocean current turbine generator performance is expected to be greatly enhanced. By adding the turbine duct housing, under the current velocity of 1 and 2 m/s, parametric studies including the duct housing type, duct entrance area, tilt angle, and duct length-to-diameter ratio are performed. After obtaining the optimized set of design values for our current design, a complete system analysis of the ocean current turbine generator was performed to provide future design guidelines.