Abstract: In order to explore the mechanical properties and damage development process of coral seawater sea sand concrete (CSSC) under three-dimensional compression, 132 CSSC cylinder specimens were designed and manufactured for conventional triaxial tests considering factors such as confining pressure and age. The results show that with the increase of confining pressure, the failure mode of the specimen changes from vertical splitting failure to oblique shear failure, the peak of the stress-strain curve is raised and the descending section is gradually gentle, and the damage development is inhibited. When the age T≤60d , the change of mechanical properties tends to be stable. When T=180d, the yield strain and yield stress increase by 8.88% and 11.64% respectively compared with that at 28d. When T=365d, the elastic modulus increases by 9.18% compared with 28d; according to the experimental data, the calculation formulas of yield stress, yield strain and elastic modulus of CSSC under different confining pressure values are proposed. The influence of confining pressure on the internal damage evolution of CSSC is significant, and with the increase of confining pressure, the influence of age on it is gradually weakened. Finally, a CSSC strength prediction formula considering both age and confining pressure is proposed, and the prediction results are in good agreement with the experimental results.