Abstract: Rock mass structure theory was a major theoretical innovation of the 20th century in Chinese engineering geology academia. In this paper,a brief introduction to the theory which has been widely applied in China since the 1970s has been done. The theory provides a theoretical basis and method to guide the resolution of major engineering geology problems encountered in a series of world-class engineering construction. From part of cases study,the rock mass structure theory,vigorously promoted by the authorities as industry standards,is revealed the scope of its successful application,including rock-mass stability evaluation,rock mass quality,rock slope failure mechanism and selection of foundation rock mass in a large-scale hydropower. Moreover,this paper discusses the acquisition method of main indexes about rock mass differences,quantitative indicators and aspects of its improvement. On the basis of the above study,two new sub-class rock structure,i.e.,in situ mosaic-fragmented structure and bond-layer structure,is proposed. Then their typical characteristics,disaggregated index as well as those effective applications in practical engineering are illustrated.