Abstract: In order to investigate the influence of phenolic allelochemicals on the growth and development of tobacco seedlings, effect of benzoic acid, p-hydroxy benzoic acid and salicylic acid on seedling root growth, characteristics of gas exchange, chlorophyll fluorescence parameters and chlorophyll content of tobacco were analyzed in this study. Result showed that chlorophyll content of seedling leaf (SPAD value) first increased and then decreased with the enhancement of the three phenolic acids; Three phenolic acids all significantly inhibited the growth of tobacco seedling root, such as tip number, total root length and total root surface area, which showed the trend of first increased and then decreased or decreased directly; three phenolic acids all decreased the net photosynthetic rate (Pn), there was no significant difference in the treatment of benzoic acid; three phenolic acids all had effect on chlorophyll fluorescence parameters, the Fv/Fm value decreased with the increasing of concentrations, while with no significant difference, qP and PSII values significantly decreased. Our study exhibited that all three phenolic acids inhibited the developing of tobacco seedlings and the photosynthesis activity of tobacco plant.