Abstract: Dry-wet cyclic effect is one of the primary factors attributed to the performance deterioration of cover barriers in landfills and contaminated sites. In this study, the CCL was amended with xanthan gum via wet-mixing method, and the GCL was amended with polyanionic cellulose through dry-mixing method, aiming to enhance the hydraulic and gas barrier performance of compacted clay liner (CCL)-geosynthetic clay liner (GCL) composite cover barriers under dry-wet cycles. These two liners were combined with protective soil liner to generate a polymer-amended composite cover barrier. A one-dimensional soil column model test system was developed, which was capable of simulating dry-wet cycles and evaluating hydraulic and gas barrier performance. The performance of the amended composite cover barrier was investigated and compared with the unamended barrier. The results showed the amended cover barrier exhibited an insignificant wetting peak in the 5th dry-wet cycle. In contrast, the bottom midpoint of the unamended barrier showed a significant wetting front in each dry-wet cycle. After the 6th dry-wet cycle, the gas flux of the amended barrier was measured to be 2.33×10-4 m3/(m2•s), which was 91.85% lower than that of the unamended barrier. After the model tests, scanning electron microscopy and mercury intrusion porosimetry were conducted on the exhumed CCL and GCL samples. The results indicated that two types of polymer hydrogels could effectively fill the pores of CCL and bentonite in GCL, and the pore size of the amended CCL was smaller than that of the unamended one. The gas or liquid flow channels within amended CCL and GCL was more tortuous. The results are useful to enhance the hydraulic and gas barrier performance of GCL-CCL composite cover barriers under dry-wet cycles.