Objective To observe the survival rate of reversed-flow free flap after anastomosing one venous reverse flow and to explore the change of intravenous pressure and mechanism of venous reverse flow. Methods Thefree vascularized posterior tibial flap with reversed flow was successfully established in NewZealand white rabbits.Fifteen rabbits were randomly allocated into 3 groups of 30 flaps. In group A,two vena comitans were anastomosed.In groups B and C,only onevenae comitans was anastomosed. In groups A and B,intravenous pressure was measured immediately and 30,60 and 120 minutes after anastomosing the vascular pedicle.Flap survival rate of group B was measured after two weeks. In group C, radiography of one venae comitans was observed.The diameters of posterior tibial vessels was measured on all the rabbits before anastomosing the vascular pedicle. Results The diameters of posterior tibial artery was 8.0±0.3mm and of vena comitans was 11.0±0.5 mm。The intravenous pressure of group B increased rapidly and reached its top value after about 30 minutes (P＜0.05).It then decreased and approached normal level after about 60 minutes (Pgt;0.05).The intravenous pressure was not significantly different between groups A and B in each time interval (Pgt;0.05).Two flapsresulted in avulsion,infection and necrosis.The remaining 8 flaps survived completely.Most of the radiopaque in group C flew back to the proximal tibia one hourlater. Conclusion Venous retrograde return is abundant in reverseflow free flap of anatomosing one vena comitans.The main way of venous reflux in reverseflow free flap can be through “direct incompetent valve route”.