Sudden blood in urine may be due to urinary tract infection, urinary stones, urinary malignant tumors and other diseases, but also can be seen in strenuous exercise and other physiological conditions. 1. Urinary tract infection: young patients may suddenly develop hematuria, which may be accompanied by frequent urination, urinary urgency and other symptoms. 2. Urinary stones: during exercise, stones may cut through the mucous membrane of the ureter, renal pelvis and urethra, causing local bleeding, and if small blood vessels are damaged, a large amount of hematuria will occur. Corresponding surgery can be chosen for treatment according to the location of the stone. 3. Malignant tumor of urinary system: after the rupture of malignant tumor, due to the location of the tumor with more blood vessels, spontaneous bleeding will occur, and this kind of bleeding usually doesn’t have any clinical manifestation, also known as painless hematuria. It can be treated by surgical removal of the tumor. 4. Physiological factors: blood in urine can also appear suddenly in the case of strenuous exercise, overwork, etc. At this time, it is recommended to take more rest and adjust the life style. Patients who have blood in urine suddenly should go to the hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of doctors.