Abstract: Based on geological, aeromagnetic and other data, and combined with measured physical properties of rock, the authors conducted a comprehensive research on Qilian Mountains (Zhangye and Gangcha areas) with the 1∶250 000 gravity data. The geological structure characteristics, geophysical characteristics, division of tectonic units and distribution of concealed and semi-concealed rock mass were studied. After many years’ gravity work in this area, the exploration area has reached nearly 30 000 km². This paper has studied the characteristics of Bouguer gravity field based on gravity data and has divided the anomaly units. The geological tectonic units have been redivided and the major faults have been discussed. Concealed and semi-concealed rock mass have been identified and the spatial distributions have been speculated and interpreted. The results show that the partition and stratification of the crust density structure in Qilian Mountains are obvious, and that the partition characteristics of the Bouguer gravity anomaly field are basically the same with the partition characteristics of the geological structure. The combination of 2.5D gravity section inversion confirms the new speculations. The results will provide some reference for comprehensive geological and geophysical prospecting.