There are many reasons that cause sudden hematuria in men, which may be caused by urinary tract infection, urinary stones, glomerulonephritis, IgA nephropathy, urinary tumors and so on, and the patients should seek medical help for a clear diagnosis in time. 1. Urinary tract infection: may be due to pathogenic bacteria infection, patients often have symptoms such as frequent urination, urinary urgency, urinary pain, hematuria and so on. 2. Urinary stones: may be due to the living environment, dietary habits, the presence of foreign bodies in the urinary system and other reasons for the impact of patients often have back pain, hematuria and other symptoms. 3. Glomerulonephritis: may be due to β-hemolytic streptococcal infection, genetic and other factors, patients often have hematuria, proteinuria, edema and other symptoms. 4. IgA nephropathy: may be due to infection, dietary habits and other reasons, patients often have asymptomatic hematuria, upper respiratory tract infection and other symptoms. 5. Urological tumor: if the patient has bladder tumor, prostate tumor, etc., it may be manifested as hematuria. There may also be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy.