Flaveria bidentis is a worst weed newly invaded in China,study on its stoichiometry help understanding its strategy to invade and adapt in different environments.In a green house,we studied the effect of soil N,P addition on F.bidentis plant growth,N,P stoichiometry characteristics and key plant functional trait e.g.leaf chlorophyll content.The results showed that the effect of different N or P level on leaf N:P was significantly different with equivalent N:P ratio used.Both leaf N:P and above ground biomass were reduced significantly with N,P addition increasing,also,this effect was mainly attributed to the mount of N used.When leaf N: P was larger than 23,then plant growth rate became lower,which in line with the growth rate hypothesis.Soil N and leaf N content have a positive correlation with leaf chlorophyll content of F.bidentis.Both F.bidentis leaf N(P)content and aboveground biomass were increasing firstly and falling later with soil N(P)content increasing.N and P were regarded as growth restrictive elements,when leaf N:P was below 21 and above 23,respectively.