The causes of old rotten leg are as follows: 1, primary venous valve insufficiency; 2, had acute thrombosis of the lower limb, causing damage to the valve; 3, traffic branch venous valve insufficiency; 4, trauma caused by venous wall damage. Its final cause lower limb venous valve function damage, the lumen of the red blood cells through the thinning of the vessel wall infiltration outside the vessel wall and between the skin tissue gap, resulting in skin nutrient metabolism disorders, causing dermatitis, dry skin, flaking, encounter trauma, itching, scratching the formation of calf hard to heal venous ulcers.