The current power generation is very suitable renewable energy for the application to Korean western and south coastal regions where characterized as having high current speed. Being different from tidal power generation that needs tremendous dam structure to preserve water, the current power generation utilizes the ocean current flow without damaging to estuary area and its environment. There are still many areas to understand the characteristics of current power generation for the actual field installation. As designing muti module with several rotors, the interaction between rotors will occur that would affect the efficiency and RPM of each rotor. In this study, the interactions caused by gaps between rotors in multi module are studied.