Adult bladder capacity is 300～500ml urine. Normally, people’s bladder is not completely empty after each urination, and there is usually a small amount of residual urine. The residual urine volume of a normal adult is about 10-15 ml. The amount of residual urine is closely related to bladder function. The amount of residual urine in the elderly usually increases. The increase in residual urine volume is one of the common causes of lower urinary tract infections. The bladder scanner is widely used clinically to reduce catheter-related urinary tract infections; assist in bladder function training; ensure patient comfort; improve the efficiency of doctors and nursing staff.