Abstract: Bioassay and physiological experiment were adopted to explore the allelopathic effect and mechanism of cotton on several plant receptors. Aqueous extract of cotton has allelopathic effect on Raphanus sativus, Brassica campestris, Lactuca indica, Brassica campestris, Echinochloa crusgall, Setaria viridis and Abutilon theophrasti and its inhibition effect gradually strengthens with increasing concentration. Aqueous extracts from stems,leaves and roots of cotton inhibit or accelerate seed germination and seedling growth, and activity of enzyme of seedling root of cotton. While aqueous extracts from stems and leaves of cotton are 0.02 g·mL^-1, root length, shoot length, lateral root number and dry weight of cotton respectively increase by 10.3%, 3.1%, 22.9% and 2.4% over the control. The above mentioned indexes are lower than the control by 34.4%, 39.2%, 40.6% and 19.0% respectively as the aqueous extracts are 0.1 g·mL^-1. At the same time，root activity and SOD activity decrease by 38.2% and 36.7%, while POD activity and MDA content increase by 52.3% and 36.5%. Growth indexes of plant receptors increase at low concentrations but decrease at high concentrations of aqueous extracts. The allelopathic effect of aqueous extract of stems and leaves is stronger than that of root. These findings show that cotton has autotoxicity effect which maybe one of reasons for continuous cropping obstacle of cotton. The economic yield of cotton will be improved by founding rational cultivate system.