There are many causes of pyelonephritis, mainly including medical catheterization and ureteroscopy, urinary tract obstruction and malformation, and infection of periurethral tissues, etc. However, there are also many patients who have no special triggers or causes. 1. Medical catheterization and ureteroscopy: patients who use catheterization or urinary instruments are prone to pyelonephritis. 2. Urinary tract obstruction and malformation: Urinary tract obstruction can lead to pyelonephritis, such as urinary stones, tumors and prostate hypertrophy, etc. In addition, neurogenic bladder, due to poor urination and increased residual urine in the bladder, can lead to bacterial growth retrograde to the renal pelvis, causing pyelonephritis. Urethral malformations can lead to pyelonephritis, and clinically common ones include sponge kidney, polycystic kidney, and so on. 3. Infection of periurethral tissues: Infection of the skin around the urethral opening and in the urethra can lead to pyelonephritis, such as paruresis, gynecological inflammation, circumcision and so on. In addition, patients with diabetes mellitus, kidney disease, and rheumatoid immune system and other internal diseases are also prone to pyelonephritis due to the long-term use of glucocorticoids and other treatments, low immune function, and the body’s resistance is relatively poor. There are many causes of pyelonephritis, when pyelonephritis occurs, it is recommended to consult a doctor in time, and identify the cause of the disease under the guidance of a physician and then actively treat it.