In this research, a new model, introducing the influence of the moisture content on the cohesive zone, is proposed and implanted in source code ESOPE of Cast3m. Under the external loading, the crack growth simulation is carried out using joint element which represents the cohesive interface. The separation in the cohesive interface is specified in terms of the cohesive traction-separation laws. At the beginning of a current time step, the moisture diffusion with the update crack length (precedent step) is estimated; and, mechanical properties in the whole specimen are then updated. Consequently, the moisture variation introduces an additional stress.