Abstract: This paper aims to examine the effect of water-rock interaction on mechanical property of altered rock. Rock samples from the slope are selected. Rock mechanics testing is carried out to examine the effect of different saturation-dehydration frequencies. The function is established to describe the variation pattern of mechanical properties of altered rock with the circulating effect. The influence of mechanical properties of altered rock with different circulating times is analyzed, using the concept of damage rate. The project result indicates that the mechanical properties of the altered rocks are obviously weakened by water-rock interaction. With the increase of water-rock interaction, the phenomenon is more obvious. With different circulating times, the tensile strength and the modulus of elasticity decay rapidly while the peak intensity is decaying continuously. When the degree of alteration of all rock has no difference, the degree of deterioration of tensile strength is the biggest, followed by the modulus of elasticity and minimum uniaxial compressive strength. As the degree of alteration and fragmentation increases, the degree of damage increases regarding the water-rock interaction to the mechanical properties of rock. The damage rate of tensile strength can reach 63%,the modulus of elasticity can reach 60%,as the present of peak intensity is 48%.And with the increase of saturation-dehydration circulation, the deterioration phenomenon of altered rocks is stable.