In men, there are 3 physiological strictures and 2 physiological bends in the process of catheterization, so adjustments need to be made to the strictures and bends during the process of catheterization. 3 strictures are located at the external urethra, the urethral membrane and the internal urethra, while the two bends are related to the inferior pubic bend and the anterior pubic bend, of which the anterior pubic bend can be corrected by lifting the penis later, while the position of the inferior pubic bend is fixed and does not change with the movement of the external genitalia. The position of the inferior pubic bend is fixed without changing the angle of the inferior pubic bend with the movement of the external genitalia. Therefore, after passing three stenoses and two bends, the penis is lifted first, and the prepubic bend is corrected in the process of catheterization, and then the catheter is inserted into the bladder with a syringe balloon of about 4-5 cm with moderate force through the inferior pubic bend and the three stenoses of its urethra until urine is seen. At this point, the catheter must be inserted into the bladder for about 4-5 cm to inflate the airbag, otherwise it may remain within the posterior urethra, and if the airbag is inflated hastily, it may cause damage to the posterior urethra.