Objective　To further improve the anatomic structure of the the fourth bony fiber tunnel in the dorsal side of the wrist, and explore its clinical significance.　Methods　With the help of the head-mounted magnifier, the roof, bottom, entrance and exit, inner and outer walls and contents of the fourth bony fiber tunnel at the area of dorsal wrist from 15 cadavers (30 sides) were dissected, and the relevant data were measured.    Results    The extensor retinaculum constituted the roof of the fourth bony fiber tunnel at the area of dorsal wrist; The base consisted of the deep fascia at the proximal end of the distal limit of the distal joint and the dorsal joint capsule of the wrist joint; The inner and outer side walls were composed of muscular septum extending from extensor retinaculum to deeper; Entry was between the head of ulna and dorsal side of the distal radius, and exit was at the dorsal side of the wrist; 5 tendons, including index finger, middle finger , ring finger, little finger branches of extensor tendons and index finger extensor tendons, 1 vascular nerve bundles, which is terminal branch of the posterior interosseous nerve and terminal branch of the anterior interosseous artery.     Conclusion    The roof, bottom, entrance and exit, inner and outer side walls, the adjacent and the contents and levels of the tunnel were described in detail, which is of great significance for the diagnosis of clinical wrist pain and avoiding iatrogenic injury of the contents of the tunnel.