Tidal current turbines (TCTs) are newly developed electricity generating devices. Aiming at the stabilization of the power output of TCTs, this paper introduces the hydraulic transmission technologies into TCTs. The hydrodynamics of the turbine was analyzed at first and its power output characteristics were predicted. A hydraulic power transmission system and a hydraulic pitch-controlled system were designed. Then related simulations were conducted. Finally, a TCT prototype was manufactured and tested in the workshop. The test results have confirmed the correctness of the current design and availability of installation of the hydraulic system in TCTs.