Thoracic Outlet Syndrome (TOS) is a common surgical disease, which will cause certain symptoms like neck-shoulder pain, headache, numbness of the upper limb and so on. Many of those symptoms are derived from brachial plexus entrapment. That syndrome is hard to diagnose in clinic. We need some direct evidence of the disease. Yet, the visualization of peripheral nerve like brachial plexus is still a tough problem. Presently, corresponding researches usually built their foundation on cadaver autopsy. In the study, a three dimensional (3-D) model of brachial plexus and its surrounding structures was established by segmentation of Chinese visible human (CVH) data. As a result, it is found brachial plexus went through a narrow tunnel surrounded by bone, muscle and tendon-like tissues. And, at its root and division sections that “tunnel” has been greatly compromised. Our findings indicate the potential sources and location of the disease, which may help to clinical diagnosis and treatment.