Segmentation of 3D human body is a very challenging problem in applications exploiting human scan data. To tackle this problem, this paper proposes a topological approach based on the Discrete Reeb Graph (DRG) which is an extension of the classical Reeb Graph to handle unorganized clouds of 3D points. The essence of the approach concerns detecting critical nodes in the DRG thereby permitting the extraction of branches that represent parts of the body. Because the human body shape representation is built upon global topological features that are preserved so long as the whole structure of human body does not change, our approach is quite robust against noise, holes, irregular sampling, frame change and posture variation. Experimental results performed on real scan data demonstrate the validity of our method.