Left lower abdomen and left lower back pain may be caused by urethral stone, pelvic inflammatory disease, pyelonephritis and other causes. 1. Urethral calculi: in acute stage, there is left lower back pain, which can radiate to the left lower abdomen, usually paroxysmal, accompanied by hematuria, urinary urgency, urinary pain, nausea and other symptoms. 2. Pelvic inflammatory disease: pain in the lower abdomen caused by inflammatory stimulation, accompanied by fever, abnormal vaginal bleeding, increased secretion, discharge with odor and other symptoms. 3. Pyelonephritis: located in the back of the abdomen, the pain in the left abdomen caused by infection, accompanied by the left side of the waist pain and lumbago, hematuria, pyuria, fever, nausea and other symptoms. Left lower abdomen and left waist pain may also be due to digestive tract diseases, retroperitoneal diseases and so on. It is necessary to consult the doctor in time according to the specific situation of the patient, to clarify the cause of the disease, and to carry out targeted treatment.