Urinary occult blood is also known as urinary occult blood and microscopic hematuria. It cannot be detected by the naked eye, but requires routine urine examination and microscopic observation of urine sediment microscopy of >3 red blood cells per high magnification field is called urinary occult blood. The causes of urinary occult blood are more common, such as inflammation of the urinary system, such as pyelonephritis, cystitis, glomerulonephritis, urethritis, etc. Secondly, stones in the urinary system are also a cause of occult blood, such as kidney stones, ureteral stones, bladder stones and so on. In addition, tumors of the urinary system can also cause urinary occult blood, such as kidney cancer, bladder cancer, etc. Malformations of the urinary system are also a cause of urinary occult blood, such as horseshoe kidney and duplicate ureter. There are also some special circumstances that can occasionally cause urinary occult blood, such as after strenuous exercise, or when a woman’s urine specimen is contaminated by menstruation during her menstrual period, or when she uses certain drugs. Strenuous exercise, oral use of certain medications, and menstruation should be ruled out before having a routine urine test, and the first mid-morning urine test should be retained. In summary, there are more causes of urinary occult blood, commonly inflammation of the urinary system, stones, tumors, malformations, in addition, strenuous exercise, menstrual contamination of specimens, etc. If there is urinary occult blood is recommended to review the urinary routine, and further do urological ultrasound, CT and other tests to clarify the diagnosis.