Abstract: Bioretention facilities are one of the measures widely used in sponge city construction in China. During the design, operation and maintenance of bioretention facilities, the emptying time has an important influence on the total runoff volume control efficiency and plant growth. However, there is a lack of systematic research on the influencing factors of emptying time. The effects of storage-layer height, rainfall interval, submerged-area height and structure type on the emptying time were investigated via laboratory experiments. The results showed that under the test conditions, the discharge time of the storage layer of different structure types of bioretention facilities was 10-140 min, and the complete discharge time was 6-47 h. The emptying time of the storage layer increased with the increase of the storage-layer water depth and the submerged-area height, and decreased with the increase of the rainfall interval. The emptying time of the storage layer water was affected most significantly by the storage height. The total emptying time increased with the increase of water storage water depth and rainfall interval, and decreased with the increase of submerged-area height. The rainfall interval had the greatest effect on the total emptying time. The research results could provide technical support for the design and optimization of bioretention facilities in the process of sponge city construction.