The composite liners (a geomembrane in intimate contact with a mineral liner) have been widely used as the barrier system for landfills. Diffusion is the predominant mechanism controlling organic contaminant transport within the composite liner. Steady-state diffusion of the organic compounds through the geomembrane was assumed in the models. The diffusion coefficient of the organic compounds through the soil liner was assumed a linear function of distance; and the effect of contaminant degradation was considered. An analytical solution for zero concentration on the bottom boundary was presented. Based on the proposed model, the sensitivity of the relevant parameters was discussed and analyzed. The results show that the relevant parameters have a great impact on the calculation results; and the contaminant half-life also has a great influence on pollutant migration. The proposed analytical solutions can only be used to calculate the organic contaminant through two-layered composite liners, and can be used for preliminary design of landfill composite liners.