Taiwan is with the presence of Kuroshio Current in the east part of the island. This ocean energy source is stable and rich so that it is potential to be developed and utilized. Due to maintain and water-proof of system, the design of surfaced ocean turbine system is made. However, the ocean velocity and direction will vary. The wave will change with the wind. These factors significantly affect the stability of a surfaced turbine. The investigation about the instability of a surfaced turbine is helpful for the practical design of current
power plant. In this study, the system is composed of turbine, buoyance platform, traction rope and mooring foundation as shown in Figure 1. In addition to the current velocity and wave, the gravity, buoyance, drag force of turbine structure on the stability are also great. The mathematical model of the system is presented. The coordinate of the ocean current turbine system is shown in Figure 2. The analytical solution of the general system is proposed. The effects of current velocity, wave, geometry parameters of structure on the pitching motion and stability are investigated.