Abstract: In order to preserve underground water and take good advantage of mineral resources, grouting curtain, an effective technical measure to ensure normal mining operation, is widely used to block underground water in the mines with large amount of water inflow.The strength of surrounding rock is bound to be impaired under the influence of underground water and the interruption of exploiting.In this paper, the grouting curtain of Zhongguan Iron Mine was taken as the research object.Based on the detailed analysis of engineering geology of mining area and hydrogeological data, a three-dimensional geological and numerical calculation model of grouting curtain was established to study the influence of weakening strength of surrounding rock on the stability of grouting curtain.According to the physical and mechanical parameters of rocks with different extent saturation, combining the spatial geometric information of rock mass structural planes, the physical and mechanical parameters, such as uniaxial compressive strength and elastic modulus, were calculated using Hoek-Brown Strength Criterion.The influence of weakening of surrounding rock strength on the stability of grouting curtain was analyzed using COMSOL Multiphysics numerical stimulation software.It turned out that the strength parameters of diorite and Ordovician limestone decrease with the prolongation of saturation times.After 90 days saturation, the uniaxial compressive strength, elastic modulus, cohesion and internal friction angle of diorite were reduced by 40.84%, 24.51%, 22.81% and 13.55% respectively, and the corresponding strength parameters of Ordovician limestone were reduced by 45.96%, 16.01%, 25.44% and 18.70% respectively.The degree of stress concentration in the contact area between grouting curtain and surrounding rock increased with the increase of depth.In the contact area between grouting curtain and strong permeability surrounding rock, the stiffness of grouting curtain differed greatly from that of surrounding rock, it was easy to form a high stress concentration area.With the continuous decrease of the strength of the surrounding rock in the grouting curtain, the stress difference between the inside and outside of the curtain and the stress concentration value in the contact area between the curtain and the surrounding rock also increased.When the saturation time of the surrounding rock in the curtain was less than 14 days, the increase rate of stress difference and stress concentration value inside and outside the curtain was larger.When the saturation time was more than 30 days, the increase rate of stress concentration value gradually decreased and tended to be a fixed value.In order to reduce the adverse effect of weakening strength of surrounding rock on the stability of grouting curtain, a drainage scheme combining cluster drainage holes with drainage chambers was proposed.In order to monitor the water plugging effect of the curtain and the hydraulic relationship between the fractured zone in the curtain and the surrounding rock, it was proposed to arrange water level observation holes inside and outside the curtain and in the upstream, downstream and fractured zone development areas of groundwater runoff.The results provide a basis for the stability monitoring of grouting curtain, the design of drainage scheme and the design of water level observation holes inside and outside the curtain.