Jimenez et al. [10] reported the carbon element in B4C would move to the surface of B4C when temperature exceeded 1800 K, forming a graphite layer and appearing the boron phase under the graphite layer,so we would deduced the electric conduction phase in the simulated seawater corrosion were mainly graphite and CaB6, respectively. The self-corrosion potential of graphite was higher than CaB6 phase in seawater, as a result, the graphite phase as negative pole and CaB6 phase as active pole commonly formed a primary battery, leading the B4C composite ceramic corrosion in simulated seawater even though the corrosion intensity was little.