Abstract: Allelopathy is defined as the direct or indirect harmful or beneficial effects of one plant or another through the production of chemical compounds that escape into the environment．This phenomenon exists extensively in the agroecosystem and take a role in ecosystem Intercropping of some special species is valueless because of the function of allelochem icals while some other certain species will benefit each other．The production will decrease if the crop is growing continuously because of autotoxicity and the rotation of proper species will avoid this result The development and application of plant-based pesticides and soil antiseptic are becoming the research focus，too．And we can use less pesticide if we try to select and cultivate crops with allelopathic genes those can inhabit the growth of weeds by intercross or gene transfer technology as well as the intercropping of common crops with the species which can control weeds，Furthermore，allelochemi．cals can be used directly as herbicides and the possibility of artificial synthesis and chemical modification will be investigated so that the pollution to the environment from chemical herbicides can be reduced．