Using pot-cultured Polygonum capitatum Buch.-Ham. ex D. Don as materials, effect of different concentration of Methyl Jasmonate（MeJA） on photosynthesis and chlorophyll fluorescence characteristics of leaves was studied in the paper. The result showed that Pn, Gs, Tr, Ci, Y（Ⅱ）, F_v/F_m, Fm and qP of Polygonum capitatum Buch.-Ham. ex D. Don increased at first, and then decreased when the concentration of MeJA changed among 0-7.5 mmol/L. F₀ has increasing tendency and NPQ has a decreasing tendency. When the MeJA concentrations was 0.5 mmol/L,Pn, Gs, Tr, Y（Ⅱ）, F_v/F_m, and Fm were the highest. However, Ci was the highest when MeJA concentrations was 0.1 mmol/L. If MeJA concentration was lower than 0.5 mmol/L, the F₀ and NPQ was stable. F₀ increased and NPQ decreased when MeJA concentration was 0.5 mmol/L to 7.5 mmol/L. In summary, the data presented in the paper suggested that MeJA treatment of 0.5 mmol/L might significantly enhance the photosynthetic efficiency of Polygonum capitatum Buch.-Ham. ex D. Don. The concentration of MeJA higher than 0.5 mmol/L did not cause significant damage to the photosynthetic system of Polygonum capitatum and the decrease of Pn was related to stomatal factors at this time.