In order to find the reason that the obvious continuous cropping obstacles found in peanut, experiment was designed to study this phenomenon in this paper. The soil samples were collected from four adjacent continuous cropping peanuts field in red soil of south China which were continuously cropped for 3,6,10 and 15 yeras respectively and the control was the abandoned farmland belonging to the same parent material at March 20, 2009. Subsequently, the kinds and content of phenolic acids of continuous cropping peanuts field were detected. The results showed that three exogenous phenolic acids of p\|hydroxybenzoic acid, vanillic acid and coumalic acid and their mixture at three different concentrations affected on the incidence of peanut seed infected with Fusarium solani and the incidence of peanut seed germination infecting with F. solani, and the growth and protecting enzymy activities of peanut seedlings by tissue culture. The results also revealed that soil p\|hydroxybenzoic acid, vanillic acid and coumalic acid accumulated gradually with the increasing year of continuous peanut cropping. The total amounts of three phenolic acids reached 11.09mg?kg- 1dry soil after 10 years cropping, which was significantly higher than that after 3 or 6 years cropping and similar to 15 years cropping. However, the amounts of coumarin and benzoic acid were very low in all detected soil samples. Plant height and root length were inhibited with all the treatments. The underground fresh and dry weight of peanut seedlings were promoted at lower level and inhibited at higher level of phenolic acids. The aboveground fresh and dry weight of peanut seedlings were inhibited at all levels except that vanillic acid and coumalic acid promoted at lower level. In addition, root activities of peanut seedling decreased and plant Superoxide dismutase (SOD) activities, Perpxodase (POD) activities and Malondialdehyde (MDA) contents rose with increasing concentration of phenolic acids comparing with the control. This result showed that the cell membrane of peanut seedling was destroyed and induced the defense reaction and this maybe provide some invasion ways to pathogen. Comparing with the control of peanut seeds treated with F. solani spore suspension, the incidence of peanut seed infected with F. solani increased and the incidence of peanut seed germination reduced with increasing concentration of phenolic acids. These results indicated that phenolic acids could inhibit the growth of peanut seedling, increase the incidence of peanut infected with pathogen and decrease the incidence of peanut seed germination infecting with pathogen. Phenolic acids existed in continuous peanut cropping soils would destroy the cell membrane of peanut seedlings, and then the peanut pathogen invaded the seedlings. This would led to the inhibition of peanut seedling growth, and continuous cropping obstacles would happen.