The construction of additional cut-off wall is a common reinforcement method for earth rock dam.At present,there are few studies on whether the construction of additional concrete cut-off wall will affect the stability of dam slope in the risk removal and reinforcement project of earth rock dam,and there is little consideration for engineering design.In order to analyze the impact of the additional cut-off wall on the dam,a numerical calculation model is established by using the finite element method to analyze the variation law of dam seepage and stress field before and after adding the cut-off wall,and the stability of dam slope under different operating conditions.The calculation results show that after the addition of cut-off wall,the phreatic line of upstream dam slope rises and that of downstream dam slope decreases obviously;The pore water pressure of the soil in front of the wall is greater than that behind the wall,and the effective stress of the soil behind the wall is greater than that in front of the wall;The stability safety factor of the upstream dam slope decreases after the construction of the cut-off wall,but the reduction range is small.Compared with the upstream dam slope,the construction of the cut-off wall has a more significant impact on the stability safety factor of the downstream dam slope,and the safety factor has increased by nearly 10%;The faster water level sudden drops,the faster the stability safety factor of upstream dam slope decreases,and the smaller the minimum stability safety factor of dam slope reached by sudden drop,which is more unfavorable to the stability of dam slope.