While individuals of a plant community competition to the above and belowground spaces, they always affect the growth and development of neighbor plants by releasing secondary substances produced by metabolism themselves, as results of succession and adaptation of plant population to the changing environmental conditions. The results of the influence can be showed in form of accelerating or inhibitting. Allelopathy is one of the main reasons influencing the distribution of plants, formation and succession of plant community, as well as the growth and physiological metabolism of plant individuals, including metabolism processe and circulation of nutrient and energy. Allelopathy is generated directly by secreting chemical substances from roots, eluviating chemical substances from leaves and volatilization from all organs etc. It can indirectly produced by dissolving of dropped plant organs via soil microorganism. In artificial ecosystem, plant allelopathy is the foundation of vegetation restoration, intercropping in agro-forestry ecosystem.Walnut (Juglans. regia. Linn.) originates from Xinjiang China, and is cultured in large area throughout our country. Because of its important commercial values, it is essential species for the establishment of agro-forestry ecosystem. In praxis, all of the foliage, root and fruit peel of walnut can produce great deal of chemical compounds to inhibit the growth of neighbor plants significantly. But previous studies on walnut were focused on walnut cultivation and the chemical composition of the root bark and fruit peel, allelopathy of walnut foliage was not reported. In this dissertation, the chemical component and the allelopathy of walnut foliage of the varietyXi-Luo 3, the most cultured specie in our country, were studied.The research results are summarized as follows:1. We have got five kinds of compounds from the extracts of walnut foliage through extraction with solvent, isolation with column chromatography. By measuring the physical constants, chemical qualitative reaction and spectroscopy determine (1HNMR, 15CNMR, UV, EI-MS, FAB-MS, HSQC), we initially confirmed the compounds as follows: compoundⅠ: kaempferol compoundⅡ: kaempferol-3-0-arafuranoside compoundⅢ: kaempferol-3-0-arafuranoside