Possible causes of hematuria after catheterization: 1, insufficient lubrication of the urethra during catheterization, local mucosal injury during catheterization and bleeding, relatively small amount of bleeding, manifested as the initial hematuria, and the subsequent urine is normal color, this situation is more common. Patients do not cooperate in the process of catheterization, urethral spasm, resulting in bleeding from local mucosal injury during intubation. This situation only need to drink more water, hematuria can gradually disappear. 2, acute urinary retention patients catheterization due to release urine too fast, bladder pressure suddenly drop, resulting in local mucosal epithelial blood vessel rupture bleeding. This situation is the most common, for patients with urinary retention after catheterization need to regular, quantitative urination. Such as 300ml of urine each time, every hour after the urination again, can make the bladder pressure gradually decline, will not lead to acute decline in blood vessel rupture bleeding.3, urinary catheterization process of urethral injury can also lead to bleeding, this time not only the blood in the urine, the urethra can also be seen at the mouth of the drop of blood, this situation is mostly due to urethral injury.