On an Artificial Soil Rapid Infiltration(ASRI)system,a new effective method for disposing domestic wastewater,mechanisms of COD removal in the system were studied.The result showed that COD removal in ASRI contributed to biodegradation and abiotic interception when wastewater was flooding the bed.Abiotic interception such as physical infiltration,adsorption and soil fixation intercepted and captured COD in the ASRI bed,in which the COD was decomposed when the water was drained.Periodic monitoring of organisms showed that both aerobe and anaerobe,which came from soil and sewage,played an important role in COD removal and aerobic biodegradation was the dominant action in the whole cycle of the ASRI system.