Abstract: It is necessary to elucidate its growth mechanism in order to prevent and control the further spread of Flaveria bidentis, an invasive plant in China. The effects of shading (shading rate of 0, 50% and 80%, respectively) and planting pattern (single cropping of F. bidentis, single cropping of Chenopodium album and their intercropping) on germination rate, fluorescence characteristics and growth characteristics of the two plants were investigated. The results showed that moderate shading contributed to emergence rate, but emergence rate of F. bidentis was not uniform, which was one of important factors as a stronger invader. With the increasing light intensity, net photosynthetic rate (P_n), photochemical quenching (q_P), electron transport rate of PSⅡ(ETR), quantum yield of PSⅡ(Y), nonphotochemical quenching (q_N), water use efficiency (WUE), shoot biomass rate (SMR), crown width (CW) and dry biomass (DM) increased, specific leaf area (SLA) decreased, LMR of F. bidentis significantly increased, LMR of C. album changed insignificantly, and the increment of DM of F. bidentis was higher than that of C. album. In 80% shade treatment, P_n and DM of F. bidentis were lower than those of C. album. In natural light treatment, P_n, q_N, WUE and relative competitive index (RCI) were the highest, CW and DM of intercropped F. bidentis and P_n, Y of C. album were significantly lower than that of the respective single treatment. F. bidentis had higher light saturation point (LSP) and light compensation point (LCP). In conclusion, the shadetolerant ability of F. bidentis was weaker than that of C. album, but it was reversed in natural light treatment. The two plants adapted to the weak light in 80% shade treatment by
 increasing SLA and decreasing LMR. F. bidentis improved competition under natural light by increasing SMR and decreasing CW.