Abstract: Widely distributed on the surface of the Earth, soil mass is a kind of quite complex natural solid bodies. This paper identifies the soil mass to have seven scale-levels of structural hierarchies. Based on the functions of each scale-level structure, the paper further describes the dialectic relationships among the different scale-levels of soil structure system from the point of view of systems science. The examination includes the basic function form the lower scale-level to the higher scale-level, the influence of the higher scale-level on the lower scale-level, the synergism of the higher and lower scale-levels, interlacing, overlapping and evolvement of the different scale-levels. The structural system can simplify complicated problems if the soil mass is regarded as a system and then divided into reasonable hierarchies for analysis during scientific research and engineering practice related to soil mass. Thus the engineering properties and corresponding formation mechanisms of soil mass can be comprehensively and correctly understood.