Clinical insertion of a urinary catheter is a catheterization procedure, a method of inserting a catheter from the external urethral orifice through the urethra and into the bladder for the purpose of draining urine. The purpose of catheterization is to help patients with urinary retention to drain urine to relieve pain, as well as to check the function of the bladder, measure bladder capacity, bladder pressure, and the amount of urine remaining in the bladder. Clinically, catheterization is used for the treatment of urinary retention, bladder instillation medication, preparation for abdominopelvic surgery, and monitoring of urine output in critically ill patients. In addition, urinary catheterization is also required to perform urodynamic tests, obtain contamination-free urine specimens, and perform cystography. Complications of catheterization include urethral injury and urinary tract infection. Urethral injury is a physical mechanical injury caused during catheter insertion, while urinary tract infection is mainly a retrograde infection via the urethra. Contraindications to catheterization mainly include acute urethritis, acute prostatitis, prostatic hypertrophy, female menstruation, urethral injury, urethral fracture, and urethral stenosis. Therefore, the patient must go to the regular hospital by professional medical personnel for catheterization operation to avoid adverse consequences.