Free flaps are a type of surgical flap and are one of the main methods of clinical surgical wound repair. A piece of skin and subcutaneous tissue is cut from a certain part of the patient’s own body to cover and repair the trauma through transposition or transplantation, and this process of skin and subcutaneous tissue is collectively known as skin flap. A flap that can be completely separated from the donor area while retaining a small network of blood vessels for anastomosis and ultimately anastomosing to the recipient vascular network is called a free flap. The main characteristic of free flaps is that the flap is transposed or transplanted with a wide range of proportional selectivity of the flap cutout size. There are two main points to consider when designing a flap: the perfusion pressure of blood vessels in the donor area and the perfusion pressure of small arteries in the recipient area. The most commonly used technique is microsurgical vascular anastomosis, in which the small vessels within the flap are anastomosed to the small arteries and veins in the recipient area. The shorter the anastomosis time for transplanting a free flap, the faster the establishment of blood circulation and the higher the survival rate of the flap. The advantage of the free flap is that it can be used to quickly repair any wound in the body in one or two surgeries. Patients should be aware that the intraoperative operation of the free flap is highly dependent on microsurgical equipment, and the risks of free flap surgery include hemorrhagic disorders, flap infection, necrosis, and inactivation. Free flap surgery requires a high level of microsurgery and should be performed in a regular, qualified and experienced hospital.