Blood in the urine once or twice may be caused by functional hematuria, urinary stones, urinary tumors, acute glomerulonephritis and other factors. 1. Functional hematuria: such as strenuous exercise, resulting in localized breakage of the urinary tract bleeding, will make the urine with blood, may also be accompanied by mild pain, pay attention to rest, generally be able to recover on their own. 2. Urinary stones: for example, bladder stones, position change or urination, the stone may cause damage to the bladder, will occasionally appear hematuria, may also be accompanied by urinary pain, urination difficulties and other abnormal performance. 3. Urological tumors: for example, bladder tumor, in the early stage, the tumor surface tissue necrosis and bleeding will occasionally appear hematuria, with the aggravation of the lesion, hematuria may occur frequently. 4. Acute glomerulonephritis: 50% to 70% of cases have hematuria under the naked eye, which usually turns into hematuria under the microscope after 1 to 2 weeks. At the same time can be accompanied by proteinuria, edema, hypertension, impaired renal function and so on. There are many other reasons for the appearance of blood in the urine once or twice, it is recommended that the patient to the regular hospital, under the guidance of the physician standardized treatment.