River and floodplain compose a whole environmental system as they have hydrological and ecological connection,and thus a scientific concept of river-floodplain environmental systyem is established and analysed.The main characteristics of river-floodplain environmental system include the followings: wholeness maintained by flooding,spatial and temporal heterogeneity,openness,complexity and fragility.Flooding plays key roles in maintaining wholeness of the river-floodplain environmental system,and the system responds to process and functions of flooding.The river-floodplain system is enfluenced by both natural process and human activities.