There are many reasons for the soreness on the left side of the waist, and the common ones are lumbar disc herniation, lumbar muscle strain, acute nephritis and other diseases. 1. Lumbar disc herniation: due to the degenerative changes of lumbar disc, part of the annulus fibrosus will be ruptured, and the nucleus pulposus will protrude or prolapse to compress the peripheral nerve roots, which can cause pain in the lumbar region, often accompanied by pain, numbness and weakness in the buttocks and lower limbs of the one side, and so on. 2. Lumbar muscle strain: due to heavy physical labor, excessive exercise and other factors, prolonged pulling and stimulation can lead to chronic strain of lumbar muscle ligaments, resulting in soreness and pain in the left lumbar region. 3. Acute nephritis: when acute nephritis occurs, due to the significant increase in the volume of the left kidney, it may cause soreness and pain on the left side of the waist due to the pulling of the peripheral membrane of the kidneys, which is often accompanied by hematuria, proteinuria, hypertension and other symptoms. Soreness on the left side of the waist side may have other causes such as kidney stones, etc. It is recommended to go to the hospital in time, identify the cause of the disease, and standardize the treatment under the guidance of the doctor.