Pain inside the left side of the waist is generally due to ocular myofibrositis, and may be caused by urinary stones, lumbar spine fracture and lumbar spine tumor. 1. Myofibrillitis: the muscles of the human waist are very rich, so under the influence of cold, tiredness, excessive pressure on the waist and other factors, it will make the muscles of the waist appear aseptic inflammation, resulting in pain in the waist. The scope of pain is generally more limited, but the pain is significantly aggravated during activities, especially when exerting too much force on the waist. 2. Urinary stones: patients with ureteral stones on the left side of the ureter, there will also be pain on the left side of the inside of the situation, the nature of this pain is colicky, the doctor needs to carry out on the patient to the abdominal CT, ultrasound and other examinations, in order to clarify the diagnosis. 3. Lumbar spine fracture: the fracture of lumbar vertebrae or the transverse process of left lumbar vertebrae can be caused by trauma or violence, and the pain on the left side of lumbar vertebrae will appear after the fracture. 4. Lumbar spine tumor: if there is vertebral tumor or metastatic cancer in the lumbar spine, the tumor will invade the vertebral body and cause bone destruction of the left lumbar vertebral body, which will lead to the pain in the left side of the waist. Diseases that can cause lumbar pain on the left side also include herpes zoster, sacroiliac arthritis and gastrointestinal perforation, etc. If the above methods still fail to relieve the lumbar pain, go to the hospital for examination in time, and carry out the treatment under the guidance of the doctor.