Abstract: The composition,growth and withering,dominant species and eco niches of the weeds in rice fields in Shenyang were investigated.The results showed that Echinochloa crusgalli,Bidens frondosa,Ammannia arenaria,Ludwigia prostrata,Eleocharis acicularis,Myosoton aquaticum,Rorippa islandica and Centipeda minima.Echinochloa crusgalli and Bidens frondosa are the main eco damaging populations in paddy fields of the area.Based on the calculation of time,horizontal and vertical breadth eco niches of the weed community, Echinochloa crusgalli and Bidens frondosa are the dominant species.Their niches overlap extensively.Mono application of barnyardgrass killing herbicide can induce spreading of broadleaf weeds such as Bidens frondosa .