Ocean current energy is mainly utilized for power generating. As an important new force of renewable energy source, it is being substantially developed worldwide. As the ocean current energy generator unit runs in seawater perpetually, design of sealing system for it is crucial. In this paper, the protective sealing system against seawater is designed for a 300kW ocean current energy generator unit in Zhoushan sea area. The sealing system includes mechanical sealing parts and detecting sensor parts. The mechanical sealing parts mainly prevent seawater leakage and the function of detecting sensor parts is mainly to send out alarming signal to the danger of leakage. The double protection of the two parts can guarantee the ocean current energy generator unit running safely in the sea water.