Abstract: To investigate the service behavior and water-storage capacity of capillary barrier cover systems in semi-humid areas of northwest region of China, a full-scale cover system is constructed in Xi'an, and the rainfall and long-term serviceability monitoring tests are conducted. The results show that: (1) Under lush vegetation growth in summer, the water release rate with vegetation is significantly higher than that without vegetation, with the former (45.80 mm) being 1.73 times greater than the latter (26.55 mm). (2) Under light to moderate rainfall conditions in the northwest region, the measured water-storage capacity is approximately 93% of the theoretical one. The soil cracks and other preferential flow pathways have the minimal impact on the impermeability performance, with leakage primarily occurring when the actual water-storage capacity exceeds the theoretical value. During short bursts of heavy rainfall, the measured water-storage capacity is approximately 73% to 84% of the theoretical one. The soil cracks preferentially infiltrating are a common and frequent induction mechanism for leakage in the soil cover layer. This may result in the inadequate utilization of water-storage capacity of soil. It is suggested that a safety margin coefficient of 1.1 to 1.3 should be considered to enhance impermeability.