Objective To provide anatomy evidence of the simple injury of the deep branch of the unlar nerve for cl inical diagnosis and treatments. Methods Fifteen fresh samples of voluntary intact amputated forearms with no deformity were observed anatomically, which were mutilated from the distal end of forearm. The midpoint of the forth palm fingerweb wasdefined as dot A , the midpoint of the hook of the hamate bone as dot B, the ulnar margin of the flexor digitorum superficial is of the l ittle finger as OD, and the superficial branch of the unlar nerve and the forth common finger digital nerve as OE, dot O was the vertex of the triangle, dot C was intersection point of a vertical l ine passing dot B toward OE; dot F was the intersection point of CB’s extension l ine and OD. OCF formed a triangle. OCF and the deep branch of the unlar nerve were observed. From May 2000 to June 2007, 3 cases were treated which were all simple injury of the deep branch of the unlar nerve by glass, diagnosed through anatomical observations. The wounds were all located in the hypothenar muscles, and passed through the distal end of the hamate bone. Muscle power controlled by the unlar nerve got lower. The double ends was sewed up in 2 cases directly intra operation, and the superficial branch of radial nerve grafted freely in the other 1 case. Results The distance between dot B and dot O was (19.20 ± 1.30) mm. The length of BC was (7.80 ± 1.35) mm. The morpha of OCF was various, and the route of profundus nervi ulnaris was various in OCF. OCF contains opponens canales mainly. The muscle branch of the hypothenar muscles all send out in front of the opponens canales. The wounds of these 3 cases were all located at the distal end of the hook of the hamate bone, intrinsic muscles controlled by the unlar nerve except hypothenar muscles were restricted without sensory disorder or any other injuries. Three cases were followed up for 2 months to 4 years. Postoperation, the symptoms disappeared, holding power got well, patients’ fingers were nimble. According to the trial standard of the function of the upper l imb peripheral nerve establ ished by Chinese Medieal Surgery of the Hand Association, the synthetical evaluations were excellent.Conclusion Simple injuries of the deep branch of the unlar nerve are all located in OCF; it is not easy to be diagnosed at the early time because of the l ittle wounds, the function of the hypothenar muscles in existence and the normal sense .