Thigh vein thrombosis may cause cyanosis. Thigh vein thrombosis can be caused by trauma, prolonged bed rest, or tumors. When thigh vein thrombosis occurs, the blood flow is poor, and some of the tissues are bruised, resulting in cyanosis of the skin of the lower extremities, which is manifested as cyanosis. In addition, it may be accompanied by lower extremity edema, pain and other symptoms. Thigh vein thrombosis can be treated with low molecular heparin sodium injection, warfarin sodium tablets, rivaroxaban tablets and other medications, and also with femoral vein incision thrombectomy or cannulation thrombolysis and other ways of auxiliary treatment, a two-pronged approach, which can play a very good role in the treatment. Patients are advised to go to the hospital for regular checkups, and if there is any abnormality, they should be treated according to the doctor’s instructions.