Urinary tract infections are caused by direct infection of the urinary tract by bacteria and viruses. If the inflammation is poorly controlled, retrograde infection can occur, which means that the infection spreads from the lower to the upper end of the urinary tract, leading to inflammatory nephrotic changes when it reaches the kidney tissue, which can develop into nephrotic syndrome, while repeated infections can form renal scarring, which can lead to secondary hypertension and chronic renal failure in severe cases. It varies with age and urinary sensation site and has three main manifestations: pyelonephritis, cystitis and asymptomatic bacteriuria. 1, pyelonephritis Infants and young children account for the majority of the symptoms of systemic infection poisoning as the main manifestation, often with fever above 38.5 ℃, high fever may have convulsions or chills, along with general malaise, atrophy, pallor, vomiting, nausea, light diarrhea. Older children report hypochondriacal or lumbar pain and percussion pain in the kidney area. Newborns show as sepsis, with weight loss, feeding difficulties, jaundice, agitation, fever or temperature not rising. 2. Cystitis Mostly in older girls, there are symptoms of frequent urination, urgency, difficulty in urination, incomplete urination, lower abdominal discomfort, pain in the suprapubic area, urinary incontinence, sometimes foul-smelling urine, and eczema of the vulva. Cystitis usually does not cause fever. 3, asymptomatic bacteriuria Asymptomatic bacteriuria refers to positive urine cultures in children without any clinical symptoms of infection. It is almost exclusively in girls, but may develop into a symptomatic urinary tract infection if left untreated. Urinary tract infections have the highest incidence in infants and children, and for inflammatory changes in the kidneys due to infections, they may lead to the occurrence of nephrotic syndrome, which not only affects the efficacy of hormones, but is often one of the triggers for recurrence or recurrence of kidney disease. Therefore, infectious diseases should be treated actively in order to effectively prevent the development of nephrotic syndrome.