Objective　To investigate the anatomical and histological structure of the sheath of thoracic, lumbar and sacral nerve roots as well as their distribution, and to explore the clinical significance.  Methods　Seven adult cadaveric spine specimens were dissected to observe the way out of the dural sac of the nerve root sheath of different segments, and to prepare sections to observe the structure of the nerve root sheath under the light microscope.　Results　There were one-hole and two-hole nerve root sheaths both in thoracic and lumbar segments, while there was only one-hole nerve root sheath in sacral segments; the one-hole nerve root sheath could be classified intoⅠtype and Ⅱ type because of the different structures inside. Compared with the other sites of the nerve root, there were only several layers of collagenous fibers being loosely connected with each other in the ganglion. The dural sleeve of ganglion at lumbar 4/5 and sacral 1~5 segments is the thinnest (F=37.31，P<0.01). And the space under the sleeve does not disappear until the ganglion.　Conclusion　The distribution ofⅠtype and Ⅱ type nerve root sheath accounts for the phenomenon of patients presenting early sensory and motor dysfunction at the same time when compressed. And the dural sleeve of ganglion at lower lumbar and sacral segments is the thinnest, which is related with the high incidence of the lumbocrural pain. The nerve root transforms into the peripheral nerve from the ganglion.