Abstract: Allelopathy of aqueous extracts from Phragmites communis leaves on the growth and photosynthetic physiological characteristics of invasive plant Solidago canadensis was determined at different concentrations \[0 (CK), 0.025 g·mL^-1 (2.5%), 0.05 g·mL^-1 (5%) and 0.10 g·mL^-1 (10%)\]. The results showed that the height growth and biomass, net photosynthetic rate and stomatal conductance were not inhibited by the low concentration (2.5%) of leaf extracts, but were significantly inhibited at the high concentration (10%). The chlorophyll content, light saturation point and apparent quantum efficiency were promoted by the low concentration of extracts but inhibited by the high concentration. With the extract concentration increasing, carotenoids content increased gradually, and the dark respiration rate decreased gradually but was significantly higher than CK. Therefore, allelopathy of P. communis on the growth of S. canadensis was found through affecting photosynthesis, including chlorophyll content, leaf stomatal openness and the light response capability.