Objective To discuss the reason of skin flap necrosis caused by vascular crisis of reverse island flap of forearm posterior interosseous artery.Methods Eight-six patients who were underwent reverse island flap of forearm interosseous posterior artery for deep tissues and skin defect on the back of hand between March,2002 and April,2014 were analyzed in this study.Eleven patients had occurred skin flap necrosis,include 5 cases had completely flap necrosis caused by circulation crisis,and 6 cases had partial necrosis at the distal of the flap.Among the necrosis cases,5 cases were injured by the machine injury,4 cases by the heavy crush and 2 cases by the traffic accident.The cause of circulation crisis was analyzed.Results In the series,75 skin flaps survived completely and 11 cases had occurred necrosis,included completely necrosis with 5 cases.The reasons of flap crisis were as follows:for the completely necrosis,2 cases with variation of perforating branch of posterior interosseous artery,1 case with absence of posterior interosseous artery,1 case with vessel pedicel entrapment in subcutaneous tunnel,and 1 case with misconduct venous congestion caused by the reverse perfusion of superficial vein.The reason of circulation crisis of completely necrosis were as follows:2 cases with artery crisis and 3 of them with distortion of entrapment at pedicel and vein crisis.One case was cured through debridement,change of medical prescription and skin grafting;and 4 cases were cured with other flap repair technique.For the partial necrosis,2 cases with variation of perforating branch of posterior interosseous artery,1 case with excessively narrow entrapment at pedicel in subcutaneous tunnel,1 case with folding vessel pedicel entrapment of skin at the back of wrist,1 case with misconduct of superficial vein trunk and 1 case with intraoperative side-injury.The symptoms of circulation crisis of completely necrosis were as follows:2 cases with artery crisis and 4 of them with distortion of entrapment at pedicel and vein crisis.Four cases were cured through debridement and skin grafting,1 case was cured by the vacuum-sealing drainage (VSD) and 1 case with skin flap repair at pedicle of abdomen.Conclusion The anatomic variation of perforator vessel of reverse island flap of forearm posterior interosseous artery;narrow entrapment at pedicel in subcutaneous tunnel and distortion of entrapment at pedicel;venous congestion caused by the reverse perfusion of superficial vein;intraoperative side-injury of the pedicel of the flap;excessively folding vessel pedicel entrapment of skin at the back of wrist after surgery will cause the circulation crisis of reverse island flap of forearm posterior interosseous artery and induce the necrosis of the skin flap.