The relations of configuration and function were studied by comparing growth mass,the quality of soil physics and chemistry,water conservation,plant diseases and insect pests for Robinia pseudoacacia,Platycladus orientalis and their mixed forest at Badaling forest centre in Beijing.The results showed that: the growth mass of mixed forests is higher than that of pure forests, the quality of soil physics and chemistry is be improved,which increases the capability of water conservation.In addition,the capability of resisting plant diseases and insect pests is advanced by mixed forests.The mode is that the Robinia pseudoacacia of one line mixes the Platycladus orientalis of three lines,and the amount of Robinia pseudoacacia does not exceed 1/4,which has definite significance for forestry health in Beijing.