The early stage deterioration of anti-corrosive epoxy coating for offshore structure use was discussed theoretically and experimentally. The degree of deterioration was determined by the critical strain measured at the three-point bending of coated test specimen exposed to the marine environment. The relation between this critical strain ε_c and the detached area S and the deflection at cracking δ _c of the coating at the three-point bending was theoretically calculated and it showed fairly good agreement with experimental data. Based on the assumption about 6, mentioned above and also on the assumption that the deterioration velocity of coating obeyed to the usual thermo-chemical reaction velocity law, the accelerating effect of several kinds of accelerated deterioration test methods were evaluated quantitatively. Finally the deterioration phenomena of epoxy coating in an early stage was schematically shown for the changes of critical strain, volume resistivity and alternating current resistance against the exposed period.