The weight and length, width and height of three directions of cuboids’ type calcareous mudstone after infiltrated with water in different period of time were measured by using electronic balance and vernier caliper. The results show that the calcareous mudstone expansion strain is proportional to volume and mass water content. Mchanical properties of calcareous mudstone were studied by uniaxial compression experiments of calcareous mudstone with different water content which carried out by using microcomputer controlled electro-hydraulic servo compression testing machine control system of YAW series. It is concluded from experiment result that calcareous mudstone is brittleness with low water content but when water content reaches saturation, calcareous mudstone presents plastic features. Based on the results above, the constitutive equation of rock considering humidity field is derived which provides important guiding significance to engineering practice.