Corrosion rate of steel embedded in coral aggregate concrete(CAC) exposed in simulated seawater for 270days and its surface free chloride(Csf) values were determined by linear polarization resistance(LPR) method and two dimensional chloride diffusion model. The chloride threshold value(CTV) of different types of steels in CAC was determined by the relationship between the Csf and its corrosion rate. The results indicate that the corrosion rate of steel in CAC gradually decreases with the increase of cover thickness and the anti corrosion performances of them is ranked as follows:2205duplex stainless steel(2205S)＞316L stainless steel(316L)＞organic coated steel(OCS)＞ordinary steel(OS). And the CTV values of them in CAC are determined as follows:Less than 0210%(OCS), 0330%0410%(316L) and more than 0463%(2205S).