To examine the effects of AM fungi symbiosis on competition between Flaveria bidentis and native species, an interspecific competition experiment between F. bidentis and Amaranthus retroflexus was conducted with different planting proportions (1∶2, 1∶1, 2∶1) under the impact of fungicide. The results showed that F. bidentis is highly obligate mycotrophic, and the competition pattern depended on weather there was AM fungi symbioses. With the use of fungicide, the relative yield (RY) of F. bidentis was less than 1.0 regardless of its planting proportion, whereas that of A. retroflexus was above 1.0. Meanwhile, the relative yield total (RYT) of both species was less than 1.0 across all planting proportions. Thus, it was suggested that the F. bidentis and A. retroflexus might use the same resource and the latter was a stronger competitor. The symbiosis of AM fungi increased the content of nitrogen and phosphorus in F. bidentis plants by 1.1-1.6 times and 1.1-1.2 times, respectively. In conclusion, AM fungi symbiosis could benefit the invasion of F. bidentis by regulating the competition between invasive and native plants, possibly with potential fungalmediated chemical interaction. External environment might affect the symbiosis between F. bidentis and AM fungi, at the same time, mycohrrizal associations played significant roles in the invasion of F. bidentis by relieving the stress, such as interspecific competition.