Objective To study the anatomical characteristics of sural blood vessel, and to explore the clinical effect of sural blood vessel combined with free skin flap in repairing large tissue defect of calf. Methods 10 fresh adult cadavers were col-lected for experimental studies. Chose 8 cadavers randomly and ligate the sural medial vessel (4 cases) or sural lateral vessel (4 cases) of one limb, leaving the contralateral limb un-ligated as control. Angiography was performed to observe the blood supply of the gastrocnemius muscle after the ligation of the sural medial vessel or sural lateral vessel. For the remaining 2 cadavers, the ori-gin, diameter, and location of the communicating branch of the gastrocnemius muscle were observed by macroscopic anatomy and vascular cast. The data of 19 patients with large tissue defect of calf from October 2006 to September 2013 were analyzed retro-spectively for clinical research. There were 11 males and 8 females aged from 10-40 years (mean, 32 years). 12 patients took sural medial blood vessels as recipient vessels, and 7 patients took sural lateral blood vessels. 6 patients were grafted with free chest na-vel flaps, 8 with anterolateral thigh flap, 2 with lateral thoracic flap, and 3 with latissimus dorsi flap. The areas of wound surface were ranging from 5 cm×10 cm-8 cm×37 cm. The areas of the flap dissected were ranging from 7 cm×10 cm-10 cm×30 cm. Re-sults The study found that the blood supply of gastrocnemius muscle of the calf was multifocal, and was mainly by sural artery. When the blood supply of sural artery was cut off from one side, the gastrocnemius muscle could be supplied by the communicat-ing branches between medial and lateral head of gastrocnemius muscle and the communicating branches of soleus muscle. The communicating branches were at constant anatomical locations, with larger diameter and rich branches. All the 19 cases of free skin flip transplantation were survived. Healing time of wound was ranging from 13-29 d, among which 11 cases were primary healing, and 8 were secondary healing. The follow-up duration was ranging from 12-24 months. The flaps could endure friction of certain degree. No sensory dysfunction was reported. For the cases that split thick skin graft or split-thickness thin skin flap taken from abdomen or huckle were autografted to cover the donor site, primary healing was all gained. Conclusion The sural blood vessels are deeply located in the gastrocnemius muscle at constant anatomical locations, with a long pedicle and a large diameter, and are easy to be dissected, thus they are suited for anastomosis. Sural vessel combined with free skin flip provides a new treat-ment option for the repair of large tissue defect of calf.