Sclerotherapy, first proposed by Cassaigness in 1853, involves the injection of a chemical sclerosing agent into the varicose vein to cause a secondary inflammatory response in the vein wall, followed by continuous postoperative compression to cause the vein to atrophy and subsequent fibrosis of the granulation tissue in the lumen of the atrophied vein, eventually forming fibrous cords to treat the varicose vein atrophy. In the past, sclerosing agent (liquid) was mostly applied selectively to patients with mild varicose veins such as reticular varicose veins, capillary dilation or as an adjunct to surgery, and often could not be applied to the main trunk of saphenous veins. Foam sclerosing agent is a new foamy sclerosing substance formed by mixing liquid sclerosing agent with gas. In general, we advocate trunk ligation supplemented with sclerotherapy to avoid a series of complications such as deep vein thrombosis. The Second European Conference on Foam Sclerotherapy Coordination held in April 2003 in Germany considered foam sclerotherapy as one of the effective methods for varicose vein treatment and developed a definition of safe and effective foam sclerotherapy that allows experienced physicians to apply foam sclerotherapy to treat large varicose veins including saphenous trunks. It is believed that the promotion of foam sclerotherapy has led to a revival of sclerotherapy as a minimally invasive treatment for varicose veins and that the use of foam sclerotherapy in all types of varicose vein disease is recognized worldwide for its safety and efficacy. One of the reasons affecting the promotion of foam sclerotherapy is the concern about its safety. The Second European Conference on Harmonization of Foam Sclerotherapy. Focusing on the safety of foam sclerotherapy, it was suggested that it is safe to control the dosage of foam sclerotherapy at 6 ~ 8 mL; no serious complications were seen with routine application of foam sclerotherapy up to 40 mL, but symptoms such as dry cough, chest tightness, transient ischemic shock and black haze were seen above this dosage. This is because the dissolution rate of CO2 is higher than that of nitrogen. Some studies have shown that intravenous injection of 50 ~ 100 mL CO2 can be used for the diagnosis of pericardial hemorrhage, and the injection of CO2 in the right heart did not cause serious complications and reached a single limit of 450 mL in aortography. Among the many minimally invasive treatments for varicose veins in the lower extremities, foam sclerotherapy is useful for the treatment of all kinds of varicose veins and has been proven in foreign literature to be safe, simple, economical, reliable It has become a new method of varicose vein treatment because of its safe, simple, economical, reliable and reproducible features.