Abstract: Damage mechanics of concrete are often ignored in the durability study on chloride corrosion tests of offshore engineering structures, hence the durability of structures is overrated. This paper presents a study on introducing a damage factor to combine load and corrosion in numerical analysis of the durability of offshore structures. The wetting-drying tests were carried out, and the finite element model was established in order to study the durability of prestressed concrete beams under the chloride corrosion environment and long-term loadings. The results obtained from numerical analysis agreed well with test results. The finite element parametric analysis showed that 0.2mm macro-cracks have a significant influence on the chloride ion concentration, and the effect of tensile stresses on the chloride transport is limited when macro-cracks are not present. The loading ratio affects the damage range and the extent of the structure, which in turn affects the transfer of the chloride ions in concrete. The prestress delays the development of the mechanical damage in beams at 15% and 30% loading ratios, and reduces the loading effect on the coefficient of chloride ion diffusion, which improves the chloride resistance of the member. When the loading ratio increases to greater than 45%, compared to the prestressed beam, the increase in chloride ions in the normal reinforced concrete beams of chloride ion concentration is less than 10%, which means the influence of the prestress effect on the chloride resistance of the beam is weakened with higher loading ratios.