The measurement of bladder residual urine is usually measured by ultrasonography. first, the patient holds urine and does a urinary ultrasound, then the patient goes to urinate, and after urination, the ultrasound of the bladder is done, and the measured residual urine volume is called bladder residual urine. Under normal circumstances, the bladder residual urine volume should be less than 5 ml. The presence of bladder residual urine indicates that the bladder is not fully compensated for urinary function, and the amount of residual urine is directly proportional to the degree of lower urinary tract obstruction, and the more severe the obstruction, the more residual urine volume will increase. The amount of residual urine in the bladder can be examined to determine the corresponding disease and the severity of the urinary tract obstruction. Generally, the need for bladder residual urine volume testing is for patients with abnormal bladder forceps function or lower urinary tract obstruction.