In this paper we firstly analyze internal structure（refers to structures that are hidden behind outside structures and can not be seen directly） of volumetric data based on the set theory and describe the requirement for the volume rendering method used for rendering internal structures. Based on the requirements

we propose the use of an internal structure region based volume renderer that offers an alternative for visualization of internal structures of volumetric data. The approach can analyze internal structures because it divides the volume data into two subsets: internal structure region (or local region) and context region. The internal structure region provides mechanisms to peel inside the data set for depicting information of internal structures. The user can analyze and understand any region of internal structures through interacting with the internal structure region. The proposed approach can be used to analyze volume data quantitatively and thus improve the analysis quality. The proposed approach shows powerful usefulness in 3D medical image analysis.The experiments show that the proposed approach is effective for analyzing inner structures.