Left renal pelvic dilatation means that the width of the renal pelvis becomes larger, which is mostly caused by obstruction of the urinary tract, obstruction of urine excretion, and increase of renal pressure. Clinically, there is no special symptom of renal pelvis dilatation, but it can be accompanied by some primary symptoms, such as pain in renal region, hematuria in patients with renal stone. Chronic pyelonephritis will have symptoms such as polyuria, increased nocturia and low fever. Causes of renal pelvis dilatation include urinary system obstruction, such as congenital ureteral and urethral stenosis, renal stones, urethral stones, and so on. External compression of the urinary system, such as tumors in the tissues adjacent to the bladder and ureter, and prostate hypertrophy. Inflammation of the urinary system, such as pyelonephritis. Physical examination is needed for renal pelvis dilatation: buckling, palpation; laboratory examination: blood routine, urine routine, urine culture, etc. Imaging examination: ultrasonography, X-ray, CT, etc. Pathologic examination, etc. Determine the cause of the disease and treat the primary disease. The treatment of renal pelvic dilatation is mainly to identify the cause of the disease and take measures according to the patient’s condition. For example, pethidine hydrochloride can be used for analgesia when strong colic attacks occur in patients with renal stones, and ureteral intubation or pyelotomy is needed for urinary tract obstruction to ensure smooth urine drainage and help control infection. Patients with left-sided renal pelvic dilatation should go to the hospital for timely examination and treatment under the guidance of the doctor.