Abstract: In order to study the influence of coal and rock damage on their mechanical properties during loading process and to build the constitutive equation of damage of coal and rock, single axis and three axis loading and unloading tests of coal and rock were conducted respectively. The tests results showed that with the increase of rock damage the rock unloading elastic modulus decreases, but the plastic strain increases gradually, which means that rock damage is of elastic and plastic damage. With the increase of confining pressure, the decrease value of elastic modulus is reduced, rock damage mainly increased the plastic deformation of the rock, rock damage fracture changes from brittle fracture to plastic collapse. Assume that rock damage rate is in line with Weibull statistical distribution, on the basis of this assumption, the coal and rock damage evolution equation was established, then through experiment and correlation analysis, the constitutive equation of coal and rock elastic-plastic damage was constructed. Finally the constitutive equation was used to fit the experimental curve, the fitting result verified the correctness of the constitutive equation of elastic-plastic damage.