With a hydrous limestone mine in South China as the engineering background, a study has been carried out on the water-proof effect of the grouting curtain. With a typical cross section of a limestone mine slope as the research sample, a numerical model of FLAC3D fluid-solid analysis has been established, followed by a study on the variation characteristics of slope stress, slope deformation and pore water pressure under excavation and seepage. The numerical results show that the slope stress, horizontal displacement and pore water pressure decrease with the decrease of elevation. At the same elevation, the pore water pressure on the excavation side of the slope is relatively small, which indicates that the grouting curtain can effectively reduce the water infiltration, a great significant indicator for the safe mining of open pit mining and the control of surrounding environment.