Abstract: When the ambient water penetrates into concrete, the moisture content and mechanical properties of concrete will be changed. Based on the existing experiments and theoretical models, it is assumed that the difference of dry and wet concrete strength is related to the surface energy and elastic modulus variation of material. Concrete moisture distribution is calculated by FEM software ANSYS, and compressive strength of concrete under different humidity is analyzed by a probability distribution and reliability analysis model. The results show a good agreement with that of the experiments, which can provide references for the parameter determination of concrete under real work conditions.