The aim of this work is to predict the crack propagation in wood beams under climate conditions. This work is based on Linear Elastic Mechanics equivalent Rupture. A model is developed in the finite element (FE) code Cast3M; it is based on the theory of a cohesive crack and takes into account the influence of moisture content on the fracture process zone. Monotonous fracture tests in mode I are performed on the Maritime pine under different moisture contents in order to determine cohesive zone model parameters (bilinear softening law). Fracture tests under constant load are also performed under relative humidity variations. In addition, mass transfer is integrated in the modelling to determine the moisture content at all points of the mesh as a function of humidity. The mecanosorptive behaviour of wood is also introduced in the FE calculations. The simulation has been validated by comparison with experimental results.