Leg pain and swelling is particularly serious may be caused by vascular diseases of the lower limbs, may also be trauma, infection and other factors. 1. Vascular diseases of the lower limbs: If the blood vessels of the lower limbs are diseased, it may cause the stagnation of blood in the veins of the lower limbs, increase the pressure of the blood vessels, and accumulation of metabolic products, resulting in hypoxia and anoxia of the limbs, and swelling and pain of the lower limbs, such as varicose veins of the lower limbs and vasculitis. 2. Trauma: trauma to the lower limbs will cause the rupture of small subcutaneous blood vessels in the affected area, and the contents of the blood vessels will precipitate into the tissue interstitial space and react with the body’s coagulation system and the immune system, resulting in redness, swelling, heat, and pain of the inflammatory changes, and the above mentioned symptoms may occur, such as fracture of the lower extremities, crush injuries to the lower extremities, and so on. 3. Infection: the lower limbs are richly covered with muscle, fascia and fat tissue. If the infection of the lower limbs is caused by the invasion of bacteria, viruses and other pathogenic bacteria, swelling and pain may also occur, such as cellulitis of the lower limbs, boils and carbuncles of the lower limbs, and so on. The symptoms of leg pain and swelling alone sometimes can not accurately determine the cause, but also need to be combined with the characteristics of the medical history, other test results in order to make an accurate judgment, it is recommended to clarify the cause of the disease under the guidance of the doctor, and comply with the doctor’s instructions to standardize the treatment.