The seedlings of P.cornutum(L.) Gaertn. and P.dolabratum Maxim. were used as experimental materials. Observed the growth, chlorophyll content, chlorophyll fluorescence parameters and gas exchange parameters under 0, 0.01, 0.1, 1 and 10 mmol·L-1 cinnamic acid and phthalic acid treatment. To explore the effect on photosynthetic characteristics of Pugionium Gaertn. The results showed :(1) Cinnamic acid and phthalic acid promoted seedling growth at low concentrations and inhibited seedling growth at high concentrations. The growth of P.dolabratum Maxim. was inhibited. 10 mmol·L-1 cinnamic acid and phthalic acid treatment had the most significant growth inhibition effect on Pugionium Gaertn. (2) Chl a, Chl b and Chl.a+b decreased in different degrees after treatment with different concentrations of cinnamic acid and phthalic acid. (3) Pn, Tr, Gs at 10 mmol·L-1 were significantly lower than that of the control, while Ci had no significant change. The main reasons for the reduction of photosynthetic rate were non-stomatal factors. (4) Fv/Fm、ФPSII、qP at 10 mmol·L-1 were significantly lower than that of the control and NPQ were significantly higher than control. The study found that the high concentrations of phthalic acid and cinnamic acid inhibited photosynthesis and reduced photosynthetic rate in seedlings, resulting in the impairment of PSII reaction center activity and opening in leaves of these two species, which subsequently affected the growth of Pugionium Gaertn. In addition, the effects of cinnamic acid and phthalic acid on photosynthetic characteristics of Pugionium Gaertn. were different, which might be due to different plant types and stress types.