The crust structures of Nanling Mountains has to be revealed for identifying its tectonic characteristics and formation processes. This paper presents 3D crustal density disturbance maps of the studied area, and finds information corresponding to the upper, middle and lower crustal structures respectively. Writer use a method called the multi scale analysis for delineating density disturbances of the crust at different depths. This method of regional gravity data processing combines theories based on multi scale wavelet analysis, spectral analysis of potential fields and geophysical inversions. Density disturbance maps corresponding to depths from 1.5 km to 48.6 km are obtained, showing that the Nanling Mountains is an independent tectonic unit of low density in the upper and middle crust. Writer suggest that subduction of the Tethys ocean and collision between the Eurasia plate and the Kalimantan Terrane completes the formation of the Nanling Mountains in about 100 Ma ago, and the late magma chambers of low density in the upper and middle crust represents the second magma belt of the subduction of the Tethys. The method of multi scale analysis demonstrates its power for delineation of crustal structures and 3D locations of tectonic units of the Nanling Mountains, providing new evidences for understanding corresponding intra plate mountain building processes.