Excessive limb growth and thickening is one of the clinical manifestations of congenital arteriovenous fistula, which is caused by the abnormal development of the embryonic primordium during its evolution, resulting in abnormal traffic between the arteries and veins. Congenital arteriovenous fistula, also known as congenital arteriovenous malformation, is caused by the formation of abnormal traffic between the arteries and veins during the evolution of the embryonic primordium. The most common site is the lower extremity. Although benign, congenital arteriovenous fistulas can develop and spread, often extensively invading adjacent tissues and organs and even spreading to the entire limb or part of the trunk. Congenital arteriovenous fistulas can be divided into three types according to their morphology. Type I refers to the presence of a transaxially oriented traffic branch between the arteriovenous trunk, similar to traumatic arteriovenous fistulas. Type II is the most common type of congenital arteriovenous fistula, with numerous small traffic branches between the peripheral arteriovenous trunks, often involving local soft tissues and bones. Type III is a limited longitudinal short-circuit circulation, in which blood from the peripheral artery enters the vein directly through the fistula without passing through the capillaries at all, and this type is mostly seen in the brain. Based on the history and physical examination, the diagnosis is usually not difficult. Congenital arteriovenous fistulas are associated with varicose veins. Therefore, the possibility of congenital arteriovenous fistula should be considered in young people or children when varicose veins are found without an obvious cause, especially if they are found unilaterally or in uncommon areas. The diagnosis is even more doubtful if the patient is found to have limb growth, thickening, hairiness, and easy sweating. The disease is congenital, so there are no effective preventive measures, and the diagnosis requires differential diagnosis with lesions in various areas, as well as prevention of complications. In particular, it is important to prevent the transfer of emboli through the fistula to cause other embolic diseases.