The obvious continuous cropping obstacles have been observed in Paeonia ostii planting. In order to understand this phenomenon, the present work studied the autotoxic potential of rhizosphere soil and root extract of Paeonia ostii on itself seedlings. Then, the extracts of rhizosphere soil and root bark of four years old Paeonia ostii were qualitatively and quantitatively analyzed with high performance liquid chromatography (HPLC). Based on the examined results, we researched the effects of five exogenous autotoxins of ferulic acid, cinnamic acid, vanillin, coumarin, paeonol and their mixture at three different concentrations and physiological responses on Paeonia ostii seedlings growth with pot-culture. The results showed that: (1) The aqueous extracts of rhizosphere soil and root could inhibit the root growth of Paeonia ostii seedlings (p＜0.05). These indicated that, under the controlled laboratory conditions, Paeonia ostii presented an allelopathic potential against itself; (2) Five phenolic compounds of ferulic acid, cinnamic acid, vanillin, coumarin and paeonol were detected and measured by HPLC in the rhizosphere soil and root bark of Paeonia ostii, and ferulic acid, cinnamic acid, vanillin and coumarin were reported previously as allelopathic substances; (3) Under controlled sand culture in laboratory, the height, root length, aboveground and underground biomass of Paeonia ostii seedlings could be affected by adding five substances and their mixtures in various concentrations. The growth indexes of seedlings were inhibited in moderate and higher concentration treatments, especially on root length and underground biomass, but ferulic acid and vanillin could stimulate seedlings growth in lower concentrations. The results were the accordant with observational phenomena in field that the root discolored and became putridity little by little when seedlings were transplanted in condition of continuous cropping; (4) The variability of root activities and chlorophyll contents of seedlings in all treatments were homologue, namely that root activities and chlorophyll contents were higher in lower concentration, inversely, they were lower when concentrations became higher, but there were stimulatory on root activity and chlorophyll contents of Paeonia ostii seedlings with lower concentration of ferulic acid and vanillin. These results revealed that the aqueous extracts from rhizosphere soil and root for 4 years could inhibit the root growth of its own seedlings, and suggested that the action of continuous cropping obstacles may relate with the autotoxic substances of phenolic compounds which come from itself exudates of root.