The urethra of male adults is 17-20cm long and has two bends: pubic anterior bend and pubic inferior bend; There are three narrow parts: the outer mouth, the membrane part and the inner mouth. These anatomical features should be mastered during catheterization. When inserting the catheter, the penis should be raised to make it form an angle of 60 with the abdominal wall, so as to eliminate pubic anteversion and make the catheter inserted smoothly. When the depth is about 20cm, urine can flow out and then enter 2cm.