The corrosion current density exactly pointed out the corrosion speed in polarization curve. The experimental results showed that the corrosion current density of B4C composite ceramic almost did not change in simulated seawater for three days, which seemed to imply that the corrosion reaction needs time to prepare, such as a abundant infiltration time. The corrosion current density gradually increased and took a peak at the 7th day. Because corrosion was a chemical reaction process, so it needed a large number of particles together and collide. At the7th day, there would be a mass of particles originated from B4C composite ceramic in touch with seawater, which can give rise to a higher corrosion reaction speed. As corrosion time went, the corrosion product gradually covered on the surface of B4C composite ceramic, hindering the contact of reaction particles and reducing the corrosion speed. The law which was shown in the corrosion current density curve was corresponding to the result demonstrated by Fig. 7.