A catheter is a commonly used medical device that needs to be left in place for patients who have difficulty draining urine, for some pre-surgical preparations, for patients who need to accurately record urine volume, and is not recommended if the patient has an acute urethritis, prostatitis, female menstruation, or severe urethral injury. Its operation is simple and practical. The specific method of use is sent below. At present, the main clinical use is the balloon catheter, the balloon can be filled with water or air, which plays the role of fixing the catheter to prevent the catheter from dislodging, the specific amount of injection is marked in the opening position on the side of the balloon cavity. Before catheterization, the patient is placed in a flat position, or semi-recumbent if he cannot lie flat, the urethral opening is disinfected three times, sterile gloves are worn, the appropriate type of balloon catheter is inserted into the urethra from the urethral opening and continues to be inserted for about 2 cm after urine flow is seen, and the fixed urethral tube is fixed by injecting saline or air into the balloon cavity. The drainage lumen is connected to the drainage bag. The above operation requires strict aseptic operation and needs to be done in the hospital by medical staff. In summary, catheters are widely used in medical treatment. The use of catheters is mainly for difficult urination, preoperative preparation, the need for accurate recording of urine volume, doing bladder irrigation therapy, etc., and also have their contraindications and precautions, which need to be operated by medical staff in the hospital.