There are two common causes of left kidney size reduction, one is congenital factors, congenital kidney dysplasia will appear left kidney shrinkage; the other is acquired factors, such as vascular embolism or infection, and trauma resulting in reduced blood flow to the kidney, the kidney will become smaller after time accumulation, further examination is needed to rule out related factors. The simplest thing is to check urine routine, followed by renal vascular ultrasound, ultrasound of renal artery, and also to pay attention to the presence of stones. Kidney shrinkage may also occur if it is caused by long-term stone obstruction in the left or right kidney alone.