Abstract: This paper attempts so approach the effect of swamp on river runoff under the special natural conditions of the Sanjiang plain through the establishment and analysis of the relation between annual rainfall and runoff of swampy rivers.The results of analysis show that the influence of the swamp in this area on river runoff is presented as follows:runoff volume,runoff increment,intercept of correlation curve,precipitation needed for creating surface flow,runoff during dry years and laging time of annual runoff are all related to swamp distribution.This kind of influence varies with the geomorphological location on which swamp lies,and related to climatic changes over years.The swamp distributed on piedmont dip plains and river terraces influences river runoff mainly through feed changes.Runoff increment caused by every precipitation increment in swampy basins is larger than that in non-swampy basins during continuous high-water years,while it is quite contrary during continuous low-water years.The swamp in these basins plays a part in intensifying runoff changes over years.The swamp developed on flood plain regulates runoff principally through its storage and permeable characteristics for water just as lakes and reservoirs take effect on making yearly changes of river runoff even.