Indications for catheterization: 1. urinary retention due to various lower urinary tract obstructions. 2. emergency and treatment of critically ill patients in clinical work. 3. diagnosis and treatment of bladder diseases. 4. urethral or cystography. 5. retention of uncontaminated urine specimens for bacterial culture. 6. routine catheterization before obstetrical, gynecological and other surgical procedures. 7. intravesical drug instillation or bladder irrigation. 8. , probing the patient’s urethra for strictures, and understanding what the cause of the patient’s oliguria or anuria is. In conclusion, the indications for catheterization should be strictly grasped in order to better serve the clinic.