Abstract: In order to determine whether phenolic acids in seed exudates affect the growth,development and infection behavior of Phytophthora sojae, the kinds and contents of phenolic acids in seed exudates of soybean resistant variety Williams82, soybean susceptible variety Sloan, non-host common bean Zihuayoudou and maize Suiyu23 were analyzed by High Performance Liquid Chromatography（HPLC） technique, and the effects of exogenous phenolic acids on mycelial growth, sporangia formation,chemotaxis and encystment of zoospores of Phytophthora sojae were determined. The results showed that there were differences in the kinds and total contents of phenolic acids in seed exudates of different varieties, among them the contents of the total phenolic acids in seed exudates were common bean＞soybean susceptible variety≥maize≥soybean resistant variety. The effects of phenolic acids on P. sojae were related to concentrations, and the inhibitory degrees of phenolic acids on mycelial growth and sporangia formation were positively correlated with concentrations. The phenolic acids at low concentrations(＜0.1 μg · m L^-1) attracted zoospores, while those at high concentrations(≥0.1 μg · mL^-1) repelled zoospores. The effect on encystment of zoospores showed that the higher the concentration, the more stimulation to encystments. Phenolic acids in seed exudates could be recognized by P. sojae as signaling molecules and high concentrations phenolic acids could repel the zoospores to protect crops.This study provided a theoretical basis for the control of soybean Phytophthora root and stem rot.