Flaveria bidentis was an invasive plant and Setaria viridis was its associated native plant species.The arbuscular mycorrhizal fungi gathered in the rhizosphere soil of F.bidentis during its invasion was selected.And then the effect of AM fungi on the root colonization rate,relative competition intensity,rhotosynthetic nutrient use efficiency,malonaldehyde content and antioxidant enzyme activities of F.bidentis and S.viridis were carried out in greenhouse pot.In the experiment there were 3 treatments:monoculture and mixture treatment of the two species,and each treatment including two levels:AM fungal inoculated and no AM fungi inoculated.The results showed that:(1)there were 4 genera and 10 species AM fungi in the rhizosphere soil of F.bidentis.Among them Glomus constrictum,Glomus perpusillum,Glomus reticulatum were the dominant species.The root colonization rate of F.bidentis was significantly higher than that of S.viridis.The relative competition intensity of F.bidentis was significantly reduced 29.57% after it was inoculated with AM fungi,while competition had no significant effect on S.viridis.(2)The AM fungi increased the nitrogen,phosphorus,photosynthetic nutrient use efficiency of F.bidentis,and then promoted the competitive growth of F.bidentis,while it had no significant effect on the growth of S.viridis.(3)The AM fungi has no significant effect on POD,CAT activities and MDA content of F.bidentis.The AM fungi significantly increased the activities of SOD and APX and the content of MDA,while the activities of POD,CAT and APX of S.viridis were significantly decreased.The results showed that AM fungi had different selectivity between F.bidentis and S.viridis.The colonization of AM fungi promoted the competitive growth of F.bidentis,increased the absorption of nitrogen and phosphorus,photosynthetic nutrient use efficiency,enhanced the activities of antioxidant enzymes in leaves and reduced the content of malondialdehyde of F.bidentis.AM fungi reduced the absorption of phosphorus,photosynthetic nutrient use efficiency and antioxidant enzyme activities of S.viridis.Thus the AM fungi produced laterality feedback on F.bidentis than S.viridis,which promoted the invasion of F.bidentis.