Soil polarization, as a result of long-term cultivation of mono-species tree stands, is the main cause of soil degradation that undermines the stable and sustainable development of forest ecosystems. To control soil poliarization, a fundmental way is to bring in other friendly tree species to form mixed forest or mulch the soil around the tree root with litters from trees of other species. Aiming at the mono-species conifer forests in the gullied leoss plateau, an indoor experiment was carried out incubating litters from different forests and roadside broad-leaved trees in soils collected from the humus layers of forests typical of the region. Results show that（1）litters of Pinus tabulaeformis could promote positive polarization of the soil, that increased the contents of organic matter and available P, and the count of microorganisms and improved the activities of such enzymes as dehydrogenase, phosphatase and polyphenoloxidase, while causing negative polarization that decreased the content of available N and dulled the activities of a few enzymes, such as urease and sucrase. Introducing Populus simonii and Hippophae rhamnoides into P _. tabulaeformis forest or mulching the forest soil with their litters could greatly improve properties of the soil, whereas Caragana microphylla, Robinia pseudoacia, and Quercus liaotungensis were not fit for this purpose. However, litters of Aesculus parviflora, Prunus cerasifera, Paulownia fortunei could also significantly improve properties of the soil, and no litters from other species of trees, except from Ginkgo biloba, could.（2）Litters of Platycladus orientalis forest could stimulate positive soil polarization that increased the contents of available P and K, and the count of microorganisms and improved the activities of a number of enzymes such as sucrase, dehydrogenase, phosphatase, protease and polyphenoloxidase. However, they could as well cause negative polarization that decreased the content of available N and the activity of urease. Introducing Q. liaotungensis and R. pseudoacia into Platycladus orientalis forest or mulching the soil with their litters could greatly improve properties of the soil of the P _. orientalis forest, and H. rhamnoides and C_. microphylla, were also fit for the purpose, whereas P_. simonii could only degrade the soil properties. In addition, mulching the forest soil with litters of Magnolia grandiflora, A. parviflora and Platanus hispanica could improve its properties, and litters of Cortex Eucommiae and Acer mono Maxim, could also do, but no litters from other tree species were suitable for the job. The findings of this study would be of some important theoretical and practical significance for modification of artificial mono-species forests and plantation of mixed forests.