Abstract: This paper used a train A, which was screened from rhizosphere soil of allelopathic rice and proved to have grass-depressing capacity as the study objective, identified the strain A by the morphology and molecular biology identification, showing it belongs to genus of aspergillus. Through measurement, the grass-depressing rate of the stain to barnyard grass was as high as 70%. Further investigation proved that the fermentation liquor of strain-A after diluted to 100 and 200 times could restrain the activity of key enzymes and protective enzyme in the root cells of barnyard grass during the training process, and increase the content of intracellular MDA by more than 20%.