The paper aims to identify the optimal concentration of methyl jasmonate (MeJA) that enhances photosynthetic performance without inhibiting leaf growth in Artemisia argyi. In this study, A.argyi seedlings were used as materials, and five spraying concentrations of 0, 100, 200, 400 and 800 μmol/L were set to determine leaf growth index, chlorophyll content, net photosynthetic rate and stomatal conductance. The effects of MeJA on the growth and photosynthetic physiology of A. argyi seedlings were systematically analyzed. The results indicated that 100-400 μmol/L MeJA showed no significant effects on leaf length, width, area, dry weight, dry weight per unit area, fresh weight, or fresh weight per unit area in A. argyi seedlings. 800 μmol/L MeJA significantly reduced leaf length, width and area, but did not affect dry and fresh weights per unit, indicating that high concentrations of MeJA (800 μmol/L) inhibit biomass accumulation of A. argyi seedlings by suppressing leaf expansion. Exogenous MeJA had no effect on stomatal conductance but altered chlorophyll content and net photosynthetic rate. Both 200 and 400 μmol/L MeJA effectively enhanced the contents of chlorophyll a and chlorophyll b; after treatment with 100 μmol/L MeJA, the content of chlorophyll a significantly increased, whereas after treatment with 800 μmol/L MeJA, only the content of chlorophyll b increased. In addition, treatment with 400 μmol/L MeJA alone effectively increased the net photosynthetic rate of A. argyi. These results show that 400 μmol/L MeJA improves photosynthetic capacity in A. argyi by improving the photosynthetic performance of A. argyi leaves rather than promoting leaf growth.