【Background】Flaveria bidentis has strong ecological adaptability and competition ability. It can form a single dominant population through inhibiting the growth of native species, and then leads to loss of biodiversity. 【Method】F. bidentis and its 4 companion species, Leonurus artemisia, Abutilon theophrasti, Digitaria sanguinalis and Amaranthus retroflexus were studied. Photosynthetic characteristics of F. bidentis and the four companion plant species were measured using LI6400 portable photosynthesis system. The changes of photosynthesis rate (Pn), transpiration rate (Tr) and intercellular CO2 concentration (Ci) during competitive growth between different plants and F. bidentis were also studied. 【Result】The effect of competition on the Pn of F. bidentis was tightly related with the kinds of native weeds. Fertilization promoted its Pn. Competitive growth significantly inhibited Pn of L. artemisia, D. sanguinalis and A. retroflexus and promoted Pn of A. theophrasti. Fertilization promoted Pn of the four native weeds. Competitive growth had an obvious influence on Tr of L. artemisia and A. theophrasti, but it had less little effect on Tr of the other two native weeds; Tr of F. bidentis was lower than that competed with A. theophrasti, A. retroflexus or L. artemisia. Fertilization significantly inhibited Tr in F. bidentis grown in monoculture. Ci of F. bidentis was decreased obviously when it competed with L. artemisia, A. theophrasti and A. retroflexus respectively. Fertilization addition significantly inhibited Ci of F. bidentis in monoculture treatment. 【Conclusion and significance】Fertilization affected the photosynthetic charateristics of F. bidentis. The effect of different native plant species on the photosynthesis of the invasive plant species was different. The research results would help to discover the invasive mechanism and to provide the theoretical basis to control the invasive plant species.