Abstract: Under the action of seepage, the construction defects of cutoff walls have a significant impact on the evolution process of their leakage dissolution. In order to investigate the influence mechanism of poor overlapping of the adjacent groove sections and the bottom bifurcation of the cutoff walls, based on the relevant theories of fluid dynamics and chemical dynamics, a coupling analysis model for leakage dissolution of concrete cutoff walls with construction defects is proposed. Based on a sand gravel dam project with geomembrane anti-seepage measure, the variation laws of calcium ion concentration, porosity and seepage characteristics of the concrete cutoff walls under two types of defects are revealed. The calcium ion concentration of the cutoff walls decreases with the increase of service year, and the more serious the defects are, the lower the concentration of calcium ion is. The porosity increases exponentially with the service year, and the maximum porosity increases by about 1.83 times after 100 service years. The anti-seepage performance of the cutoff walls decreases with the increase of the service year, joint width and bifurcation height of the construction defects. Compared with the intact condition of the cutoff walls, when the joint width is 3.0 cm or the bifurcation height is 3 m, the equivalent permeability coefficient of the cutoff walls increases by 8.20 times and 40.38 times respectively after 100 service years, and the total seepage flow of the dam body and dam foundation increases by 4.49 times and 5.81 times, respectively. The research results can provide theoretical support for evaluating the long-term service performance of earth-rock dams.