Urinary tract infection will not cause hydronephrosis. Urinary tract infection can cause changes such as congestion, edema and erosion of the local mucosa, but it will not lead to complete obstruction of the ureter or renal pelvis, and hydronephrosis will not occur. After anti-infection treatment, the inflammatory reaction of the local mucosa disappears, the mucosa returns to its normal form, and the patient’s symptoms of urinary tract irritation, back pain and fever disappear completely. If hydronephrosis occurs during urinary tract infection, ultrasound, CT and other relevant examinations of the urinary tract are recommended to clarify the cause of hydronephrosis. In this case, it may be caused by the presence of stones in the urinary tract or congenital narrowing of the urinary tract, or it may be caused by the return of urine from the bladder through the ureter into the kidney, which needs to be further determined by dynamic review and observation. It is also necessary to conduct pre-infection and post-infection comparisons, such as urological ultrasound or CT review after anti-infection cure, to understand whether there is any change in the effusion and to take further treatment to completely cure the hydronephrosis.