The causes of calf pain below the knee are mainly physiological factors, such as lactic acid accumulation caused by excessive exercise, pathological factors such as vascular lesions, such as thrombosis and phlebitis, lumbar spine diseases, such as lumbar disc herniation, local tumor lesions and other causes. 1. Physiological factors: mainly caused by the accumulation of local lactic acid after a large number of exercises or local muscle strain injuries, the pain can be significantly relieved after rest. 2. Vascular lesions of the lower limbs: deep vein thrombosis of the lower limbs, phlebitis or arterial occlusive sclerosis, etc., which can be clearly diagnosed by vascular ultrasound, and are usually accompanied by localized swelling. 3. Lumbar spine disease compressing the corresponding nerve root: lumbar disc herniation, lumbar spinal stenosis, lumbar spondylolisthesis, etc., usually accompanied by pain and discomfort in the lower back, which can be clearly diagnosed by lumbar spine CT and MRI. 4. Tumorous lesions in the calf area: osteoid osteoma, etc., which can be clearly diagnosed through MRI. If calf pain below the knee is not relieved after resting or recurs repeatedly, it is necessary to go to the hospital in time for diagnosis and treatment to clarify the cause of the disease.