Abstract: Most rainwater drainage pipelines in China have sediment accumulation phonomenon, which often blocks the pipeline and reduces the drainage capacity, resulting in water logging. Meanwhile, the sediment accumulation is also one of the main sources of abruptly pollution in the receiving water. In view of the above problems, the effects of sediments accumulation thickness, sediment surface roughness and pipeline slope on the drainage capacity of rainwater pipeline were studied through laboratory experiment. The results showed that with the pipeline slope of 2‰, and when pipe diameter was 150 mm, the sediment accumulation thickness increased from 20% to 70%, and the reduction rate of drainage capacity increased from 14.93% to 59.56%. According to the hydraulic similarity criterion, when the diameter of pipeline was 2 000 mm, the sediment accumulation thickness increased from 20% to 70%, and the reduction rate of drainage capacity increased from 44.78% to 73.75%. Therefore, the reduction rate of drainage capacity increased with the increase of sediment cumulative thickness and pipe diameter. The changing of surface roughness of the sediment has no markedly effect on the drainage capacity, under experimental conditions, the average increase in drainage capacity reduction was 5.93 percentage points, while the slope change had a more obvious effect on the drainage capacity. When the slope increased, the reduction range of drainage capacity was 12.30-28.83 percentage points. Overall, the research results could provide a support for the optimization design, maintenance management, monitoring and evaluation of urban rainwater drainage pipeline.