Vegetation has an important influence on soil conservation; however, few studies have reviewed the impact of vegetation on soil conservation from the perspective of plant functional traits. In this paper, we summarized the impact of above-ground and underground functional traits on soil conservation and the relationship between aboveground and underground functional traits. We concluded that:(1) The aboveground vegetation functional traits mainly control soil erosion through the effects of splash erosion and surface erosion and indirectly by changing the soil physical and chemical properties. Its functional traits mainly include leaf area, leaf length, leaf width, branch number, and vegetation height, etc.; (2) The underground functional traits on soil conservation are mainly reflected in soil retention, soil shear strength improvement, soil erosion resistance enhancement, and soil permeability enhancement. Soil retention by plant roots is closely related to the tensile capacity of the roots. The physical and hydrological properties of plant roots are closely related to the fine root ratio, root length density, and root surface area, etc.; (3) Some aboveground functional traits of plants can indirectly reflect some of the underground functional traits, but existing studies are mostly qualitative; (4) In the study of plant functional traits on soil conservation, it is urgent to strengthen the long-term location monitoring of aboveground functional traits of vegetation, deepen our knowledge of the functional traits of vegetation, especially the mechanism of root characteristics on soil conservation, strengthen the quantitative expression of functional traits in the aboveground and underground parts of vegetation, and establish a quantitative relationship between vegetation functional traits and soil conservation functions. We must strive to achieve a dynamic link between vegetation functional traits and soil conservation functional characteristics.