Abstract: Desiccation cracks of compacted clay liner might have a great effect on its hydraulic conductivity. During the decrease of its water content, its crack area ratio, length and width will increase. Desiccation cracks can be divided into the major and the minor types. There are obvious differences for the change rate of crack parameters before and after minor cracks appear. Wider cracks can't entirely heal after hydration, which reveals that the wet-dry cycling is irreversible for the compacted clay liner. Development of cracks in the clay can be monitored successfully with the Araldite that was put on the inside wall surface of the test cylinder. The Araldite can also prevent side-leakage. One wet-dry cycling can increase the hydraulic conductivity of the compacted clay liner for nearly two orders in its magnitude. Non-completely-healing cracks and microcracks might be the main reasons for the increasing of hydraulic conductivity during the wet-dry cycling.