The causes of pain symptoms in the left posterior lumbar region are as follows: 1. It may be due to changes in the pressure in the lumbar spinal canal caused by lumbar disc herniation, which is reflected to the left lumbar region through the sinus nerve, causing pain in the left lumbar region. 2. The pain may be caused by internal diseases, such as inflammation of the ureter and kidney, stones and tumor lesions, which can cause painful symptoms in the left posterior lumbar region. Sometimes the pain is very severe, and sometimes the pain is mild. Therefore, if the symptoms of left posterior lumbar pain appear, after rest and topical anti-inflammatory and analgesic medication, if there is no significant relief within a short period of time, or if the pain symptoms are progressively aggravated, you must go to a regular hospital in time to improve the necessary auxiliary examination and choose a reasonable treatment method, so that the symptoms of left posterior lumbar pain can be effectively relieved as soon as possible.