Deep vein thrombosis of the lower extremity is a common peripheral venous disease. In recent years, with the further development of interventional therapy, deep vein intubation thrombolysis has gradually become a common surgical method for the treatment of deep vein thrombosis of the lower extremity, and the vascular surgery department of our hospital adopts deep vein intubation thrombolysis via the small saphenous vein to achieve good results. 1.Treatment method 1.1 Placement method Before placement thrombolysis, patients are advised to perform temporary inferior vena cava filter implantation to prevent pulmonary embolism caused by thrombus dislodgement during placement, and explain the risks to patients and family members, and sign the consent form for refusal of treatment with family members if they refuse. None of the patients in this group underwent inferior vena cava filter implantation. Patients were placed in a lateral position toward the healthy side, with the affected limb in an extension position on the healthy limb. Using local infiltration anesthesia, a small longitudinal incision was made at the midpoint between the external ankle and Achilles tendon, approximately 3-4 cm, and the trunk of the small saphenous vein was isolated, and the trunk of the small saphenous vein was punctured under direct vision using the Seldinger technique, and a 4F catheter sheath was placed. Through the catheter sheath, the lower extremity veins were visualized, the trunk of the small saphenous vein was identified and the location of the deep vein into which it converged, and the site and extent of the deep vein thrombosis were determined. A 0.035in black loach guidewire was used to enter the deep vein along the main trunk of the small saphenous vein, and a 4F thrombolytic catheter was introduced, and the lateral hole between the two markers of the thrombolytic catheter was placed completely inside the thrombus, and a blocking guidewire was placed inside the thrombolytic catheter to fix the catheter sheath and the thrombolytic catheter, and the incision was sutured. 1.2 After successful placement of the catheter, urokinase 250,000 u was pushed through the catheter in a pulsatile way, and then urokinase and normal heparin were given continuously via a micropump at a dose of 500,000 u/d of urokinase and 5000 u/d of normal heparin, alternately. After 3 days of treatment, the thrombolytic catheter was angiographed via the thrombolytic catheter, and the position of the thrombolytic catheter was adjusted toward the distal end or the blocking guidewire was removed according to the results, and the treatment was continued. The duration of catheter placement was 5 to 7 days. During thrombolysis, the plasma fibrinogen concentration and partially activated thromboplastin time were monitored dynamically every 24 hours. If the imaging showed satisfactory thrombolysis and patency of the deep vein; or plasma fibrinogen <1g/L; or activated partial thromboplastin time exceeded 1.5 times normal; or two images before and after indicated no progress of thrombolysis, thrombolysis was finished. Remove the thrombolytic catheter and catheter sheath, and apply local pressure bandage. Continue systemic administration of urokinase 250,000 u and low-molecular heparin for 7-10 days. Change the low molecular heparin to warfarin for anticoagulation and monitor INR to control at 2~3. 2. Discussion The incidence of acute lower extremity deep vein thrombosis has continued to rise in recent years, and the hazards are possible pulmonary artery embolism in the near term and destruction of deep vein valve function in the distant term. For acute lower limb deep vein thrombosis, surgical thrombosis and pharmacological treatment are commonly used, but with the wide application of interventional methods, deep vein catheter thrombolysis is gradually carried out in clinical practice. In view of the shortcomings of this procedure, some scholars at home and abroad have started to use deep vein thrombolysis via the small saphenous vein route, and achieved good clinical efficacy. In our department, based on the reports in the literature, we use a small incision in the external ankle, expose the beginning of the small saphenous vein to puncture the sheath, and use selective cannulation technique under DSA to insert the thrombolytic catheter directly into the upper N vein along the small saphenous vein. If the catheter can enter the deep vein from the traffic branch of the calf, it can dissolve part of the deep vein thrombus in the calf and above. If the catheter fails to enter the deep vein from the traffic branch of the calf, it can enter the N vein directly along the small saphenous vein, which can also dissolve the deep vein thrombus in the N vein and above, which cannot be achieved by puncturing and placing the catheter from the N vein or femoral vein. This approach was tried in this group of patients, and not only the thrombus in the iliofemoral vein was thrombolized, but also most of the N vein thrombus and some of the calf DVT were thrombolized. This procedure does not directly puncture the deep vein, but the superficial vein, avoiding damage to the deep vein and reducing the chance of reoccurrence of deep vein thrombosis at the puncture site after extubation. Because of the fixed anatomical position of the beginning of the external ankle of the small saphenous vein, 70% converge into the N vein near the N fossa, 10% converge into the deep femoral vein, and 96.8% of the calf segment has a traffic branch with the deep vein within 30 cm above the ankle [3]. Thus the technical success of the procedure can be guaranteed. In addition, exposure puncture is not affected by limb swelling, which reduces the unreliability of blind puncture, avoids damage to surrounding tissues and nerves, and reduces the amount of radiation taken by the operator. The thrombolytic catheter enters the deep vein of the affected limb from the small saphenous vein, enabling the thrombolysis of N vein and even part of the calf deep vein thrombus, improving the efficiency of perfusion thrombolysis for deep vein thrombosis, and facilitating the direct thrombolytic treatment by catheter for mixed DVT. A review of the angiography reveals that the femoral vein is revascularized and the sinus of the valve is visualized, indicating that the thrombus is lysed and the valve is protected, thus reducing the degree of venous insufficiency in the future. During intubation and indwelling thrombolysis, the patient does not need to be prone or in a special position, and appropriate activities are not restricted, which is suitable for obese or severely edematous affected limbs, old and frail with limited mobility, and improves the quality of life during the treatment period.