A series of analyses have been carried out based on geological data uncovered during the investigation and construction of the large underground oil storage in rock cavern, including the geological causes of the joints, structure characteristics of the surrounding rock, and the correlation between rock mass structure and quality. As a result, some significant understandings and practical conclusions were obtained. First, the investigationโs standard technical methods: geophysical exploration and drilling, are effective and applicable in revealing the engineering areaโs large-scale structure. In the cavern, however, it is challenging to fully represent the structural characteristics of the surrounding rock. As a result, it is recommended that the adit survey method be used to improve precision and accuracy during the investigation period. Secondly, the existence of noticeable differences in the structural characteristics of granite from different locations is confirmed due to the influence of geological background. Therefore, the statistical distribution of joints based on data collected from a location far from the cavern may not accurately reflect the structural characteristics of the cavernโs surrounding rock mass. Finally, the closer the joints are to the ground surface, the more densely distributed they are and the more complex their geological characteristics become. As a result, the water curtains and main caverns should be designed with similar hydrogeological conditions and buried depths. Finally, because cavern engineering prioritizes hydrogeological characteristics such as surrounding rock permeability, joints with good engineering geological characteristics, such as the dense fracture zone, should be prioritized during the investigation and construction phases. This study gives the typical characteristics of large-scale faults, secondary faults, main permeable structures, secondary structural planes, and other structures of different levels in the survey and construction periods. In addition, the analysis and research methods of various discontinuities are summarized, which can serve as a reference for the subsequent similar cavern engineering practice.