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The landfill site was idealized as three-layer stratum composed of a compacted clay liner (CCL), a underlying layer and a layer of aquifer below the landfill. Based on Richards equation, the analytical solutions of volumetric water content in both CCL and underlying layer were obtained under steady-state seepage. According to the contaminant migration mechanism in the porous media, the one-dimensional computing model was established for contaminant migration in the three-layer strata including two unsaturated soil layers. The model considered nonlinear sorption of CCL and bio- degradation of contaminant migration process and bio-degradation of waste. The established mathematical model was used for carrying on the concrete computation on some hypothesis landfill sites. The studies on the calculation and analysis of variable parameters were conducted to examine the effect of all the related factors on the contaminant migration. The calculated results show that the sorption and bio-degradation of unsaturated soil have remarkable effect on the contaminant migration process, especially when the sorption and degradation of CCL are important controlling factors for contaminant migration process. When volumetric water content of unsaturated soil is large, the variation of volumetric water content has negligible influence on contaminant migration. [ABSTRACT FROM AUTHOR]