Hematuria is a common symptom in urology and is mainly divided into microscopic hematuria and carnal hematuria. Microscopic hematuria refers to elevated red blood cells found in the urine under a microscope, while carnal hematuria refers to blood inside the urine as seen by the eye. Most of the patients found hematuria are carnal hematuria. There are many causes of carnal hematuria, and the common causes are as follows. The most common cause of hematuria is urinary tract infection, such as cystitis, which in this case is mostly accompanied by frequent urination, urgent urination, painful urination, pain in the small abdomen, and in severe cases, blood clots and fever symptoms, which are less common in men than in women. In addition, urinary stones are also likely to cause hematuria. In this case, most of the pain in the lower back and abdomen is followed by hematuria, mainly due to bleeding caused by stones that damage the mucous membrane of the renal pelvis and ureter. Tumors of the urinary system are also a major cause of hematuria. Most of the hematuria caused by tumors is painless and occurs only in the middle and late stages of tumors, such as kidney cancer, bladder cancer and prostate cancer. Secondly, urinary system injury can also cause hematuria, such as urethral rupture and bladder rupture. In summary, there are many causes of carnal hematuria, which need to be combined with the patient’s medical history, accompanying symptoms, physical examination and corresponding auxiliary examinations to clarify the specific cause.