Swelling pain in the lower flesh of the right side of the waist is considered to be caused by muscle sprain, lumbar muscle strain, muscle tumor, kidney disease and so on. 1. Muscle sprain: due to improper preparation of the patient, when performing sports or engaging in heavy physical labor, it leads to sharp contraction or excessive pulling of the muscles, which causes muscle damage and swelling and pain. 2. Lumbar muscle strain: As the position of the waist is relatively low and bears large gravity, excessive weight bearing or the posture of lumbar activities is not standardized, which will lead to serious injuries to the muscles, fascia and ligaments around the lumbar spine, resulting in distension and pain in the right side of the lower lumbar flesh. 3. Muscle tumor: If the swelling and pain in the lower right side of the waist is considered to be caused by muscle tumor, the patient will have pain, often swelling and pain, and the patient should carry out muscle ultrasound and MRI diagnosis to confirm the diagnosis of the condition. 4. Kidney disease: If the patient has acute nephritis, chronic nephritis, diabetic nephropathy, uric acid nephropathy, etc., it will cause the patient to have swelling and pain in the right side of the waist. It is recommended that patients go to the hospital in time for examination, according to the results of the examination, with the help of doctors, symptomatic treatment, to avoid adverse effects on the body.