Determining the moisture influential depth in concrete under drying-wetting cycles is of great inter-est for investigation of chloride ion transport and thus the initiation of reinforcement corrosion.In this paper, the moisture transport processes during drying and wetting are modeled by diffusion and absorption.A pre-dictor-corrector implicit scheme of finite difference method is used to solve the partial difierential equations. The stability of moisture influential depth is then analyzed with the available numerical tool for both initially saturate and unsaturated concretes.The concept of equilibrium time ratio is proposed for drying-wetting cy- cles by the balance between water loss and intake during drying and wetting.According to this time ratio, drying-wetting cycles are classified into drying-dominated,wetting-dominated,and equilibrium ones.For dry- ing-dominated cycles,the drying front will penetrate gradually into material while the influential depth is de- termined by wetting;for wetting-dominated cycles,the wetting front will progress into material while the in- fluential depth is determined by drying.This classification has strong engineering implication and can give a more rational division of convection and diflusion zones of chloride ion transport.The case of concrete in marine splash zone is investigated to illustrate the application of influential depth in durability design of con- crete structures.