The influential depth of moisture transport in a concrete surface subject to drying-wetting cycles was analyzed numerically. The moisture transport was described by a diffusion model with different diffusivi-ties for drying and wetting. A finite difference scheme was developed to solve the partial differential equations. The influential depth was then investigated numerically for initially saturated and unsaturated concretes ex-posed to drying-wetting actions in marine environments using an equilibrium time ratio concept. The equilib-rium time ratio was calculated numerically for a saturated condition and the moisture influential depth is shown to be a linear function of the square root of the drying time. However, this equilibrium time ratio does not exist for an unsaturated condition and the moisture influential depth depends on the initial saturation as well as the drying-wetting time ratio. The results indicate that this model gives more realistic predictions of moisture transport of in situ structural concrete and its durability. The influential depth of moisture transport in a concrete surface subject to drying-wetting cycles was analyzed numerically. The moisture transport was described by a diffusion model with different diffusivi-ties for drying and wetting. A finite difference scheme was developed to solve the partial differential equations. The influential depth was then investigated numerically for initially saturated and unsaturated concretes ex-posed to drying-wetting actions in marine environments using an equilibrium time ratio concept. The equilib-rium time ratio was calculated numerically for a saturated condition and the moisture influential However, this equilibrium time ratio does not exist for an unsaturated condition and the moisture influential depth depends on the initial saturation as well as the drying-wetting time ratio. The results indicate that this model gives more realistic predictions of moisture transport of in situ structural concrete and its durability.