In order to research the effect of water level fluctuation on the mechanical properties of slope rock at altered zones, we carried out uniaxial compression test on rock samples from open-pit slope in Cangshang under different saturation-dehydration cycles. Moreover, we established the function which describes the variation pattern of mechanical properties of altered rock under water-rock interaction. We also analyzed the influence of circulating times on the mechanical properties of altered rock through introducing the concept of damage rate. Besides, the damage mechanism of water-rock interaction on altered rocks was also analyzed by scanning electron microscopy(SEM). The result indicated that the mechanical properties of altered rocks were obviously weakened by water-rock interaction, and with the increase of water-rock interaction, the phenomenon was more obvious; with the increase of circulating times, the elasticity modulus decayed rapidly while the peak intensity was decaying continuously. As the degree of alteration and fragmentation increased, the degree of damage increased regarding the water-rock interaction to the mechanical properties of rock, and after fifteen saturation-dehydration cycles, the damage rate of elasticity modulus reached 60%, while that of peak intensity was 45%.