Red crystals in urine are due to the presence of red blood cells in urine, which are common causes in clinical practice: first, urinary tract infection. Patients with urinary tract infections sometimes have obvious hematuria in the naked eye, or red crystals in the urine, and at this time patients also have a combination of frequent urination, urgent urination, painful urination, and even back pain and fever. Cephalosporins, penicillins, and quinolones can be used for anti-infection treatment, and the patient’s symptoms will be relieved. Second, urinary tract tumor. Patients will have painless hematuria throughout the whole process, and can be seen to have occupancy by kidney ultrasound or CT. Thirdly, urinary system injury, such as urethral injury after catheter insertion, or ureteral injury caused by external force.