Abstract: Through the eight years' study from 1975 to 1983, it is confirmed that the man-made mixed forest plantation (Locust mixed with Poplar) has the following characteristics in comparison with the pure Poplar plantation under the similar conditions:There are less forest diseases and insect pests; The stock volume per unit area is increased by 40—80%.The mechanism of the increase of production from the mixed forest plantation is closely connected with the soil ecological system, e. g. the utilization ratio of photosynthesis, by trees in the mixed forest plantation is raised, the nutrients in the soil of the mixed plantation are absorbed respectively by the deep and shallow roots of the trees; The Locust in the mixed plantation can also improve the fertility of the soil; The out-break of forest diseases and insect pests can be controlled under the environmental conditions of the mixed forest plantation as well.