Major characteristics of offshore current power generating rotors are presented. The study is focused on HAT (Horizontal Axis turbine) type generating system. To design rotors, various design principles are applied based on the prototype rotor particulars. To verify the compatibility of the rotor design method and to analyze properties of design factors, three rotor models are designed and fabricated and experimented in circular water channel. The models are designed with various blade numbers and shapes. At incoming current velocities, the rotor rpm, power and efficiency are measured and the properties of rotors are evaluated. The performance of each rotor at various current velocities is analyzed and compared. The results can be effectively applied to the design of current power generation system.