Phase Ⅱ Clinical Study of Human Umbilical Cord Mesenchymal Stem Cells in the Treatment of Venous Leg

Inclusion Criteria: 1. Age from 18 to 70, no gender limitation; 2. It met the diagnostic criteria of venous ulcer of lower limbs in Clinical Vascular Surgery (5th edition), and the following conditions were met: the ulcer lasted for more than 1 month; The wound area was between 10cm2 and 40cm2. Wound depth: All wounds were deep tissue ulcers below the epidermis. 3. Participate in the clinical study voluntarily, observe the study procedure, and observe the curative effect cooperatively. Exclusion Criteria: 1. Pregnant or lactation women; Women who have planned to have children recently (within 6 months); 2. Patients with peripheral artery disease with ankle-brachial index (ABI) \< 0.8; 3. Patients with active clinical systemic infection; 4. Serious skin wound infection is not under control; 5. low immune function and systemic failure; Severe heart, liver, lung, kidney and other important organ lesions (ALT, AST, Cr \& GT; Normal 1.5 times, congestive heart failure ejection fraction \&lt; Normal 30%) and severely impaired hematopoietic function; 6. Abnormal coagulation function or current anticoagulant treatment; 7. Systemic autoimmune diseases in the active stage; 8. With systemic organ or hematological malignancy; 9. PERSONS infected with HIV or addicted to drugs, tobacco and alcohol; 10. Have a clear history of mental illness; 11. Participation in clinical studies of any drug within 1 month prior to treatment (or the 5 half-life of the investigational drug, whichever is longer).