Abstract: Research on soil mass structural system is a comprehensive and interdisciplinary fundamental work which is of great theoretical and practical significance. It covers the whole soil mass system from macroscopic soil distribution area down to microscopic particulates from the angle of length scale. According to the principle that soil property changes with its corresponding length scale, soil mass structural system is divided into seven different structural hierarchies from macro to micro scopes in this paper. The significance, contents and research methodology of each hierarchy is explained. After the analysis on scientific meaning of a hierarchical division, several key subjects which will be met with in future research are introduced. Combining soil mechanics and engineering geology together tightly, the hierarchical division of soil mass structural system has not only cleared off some ambiguous understanding during the engineering property research of soil mass, but also laid a firm foundation for comprehensive and systematic research.