Although urethral stricture can lead to inability to insert a catheter, there are other possible causes, such as inappropriate catheter type, prostate enlargement, spasm of the urethral sphincter, and so on. 1. Urethral stenosis: mainly seen in the urethra there is trauma, history of infection, the formation of scar tissue in the urethra or deformed healing. When the catheter is inserted, the catheter cannot pass through when it reaches the narrowed area, so the catheter cannot be inserted. 2. Inappropriate catheter type: For example, for patients with a thin urethra, when choosing a thicker type of catheter for catheterization, it may not be inserted. 3. Prostatic hyperplasia: male patients in catheterization, because the prostate gland hyperplasia on the urethra caused by the pressure, the catheter reaches the prostate, it is easy to insert the situation. 4. Urethral sphincter spasm: mostly seen in the anus after hemorrhoids, perianal abscess and other surgical treatments, anesthesia after the disappearance of severe pain, resulting in reflexive spasm of the urethral sphincter, it is not easy to insert the catheter through the spasm. In summary, although urethral stenosis can cause catheter inserted into the situation, but this is not the only reason, it is recommended that patients go to the regular hospital in a timely manner to improve the examination, in order to clarify the cause of the disease, by the professional physician for the cause of the disease to give the appropriate treatment measures.