There are two ways to measure residual urine in the bladder: First, leave a urinary catheter in place after urination and observe how much urine comes out of the catheter, then use a syringe to draw out the urine from the catheter and gradually measure how much urine has not come out, that is, to measure the residual urine in the bladder. Second, to do ultrasound examination, all urine will be expelled as much as possible before the examination, and then the liquid dark area in the bladder will be measured, and the length, width and depth of the liquid dark area will be measured, and the three values will be multiplied together and then multiplied by 0.52 to represent the amount of urine in the bladder with residual urine. Residual urine in the bladder means that the bladder outlet is obstructed and the urine is not flowing.