Weeds are accompanying plants that influence the growth and production of crops in agroecosystem.With the properties of high tolerance to adverse environment,fast growing and high reproduction,weeds become important biological resource and play an important role in ecological balance in agroecosystem.Weeds can provide germplasm for crop genetically modification,can be used to develop medicines and control insect pests,can be developed as ornamental plants,and can be used as pioneer plants to restore degraded environment,promote nutrient cycling and conserve soil biota diversity.Weeds control by chemicals is the major factor that leads to weed diversity decrease.It is suggested that seeking approaches that favor to weed species diversity conservation and have no adverse effect on the growth of young trees in young orchard,building up weed species data base and develop ing benefit genes from weeds are the foci for the further studies.