Retrograde bacterial infections are those in which bacteria enter the urinary system from the urethra upward, through the urethra to the bladder and even into the kidneys or the parotid or prostate glands. Most bacteria come from the intestinal tract, with E. coli being the most common. Poor hygiene habits and sexual behavior, the body’s resistance to decline. When the body’s immune function declines, it can’t give full play to its role in phagocytosis and killing of bacteria, and even if the amount of invading bacteria is small, the pathogenicity is not strong, it can also cause infections; medical infections caused by conditional pathogens are also gradually increasing. Bacterial factors are mainly related to the virulence and number of pathogenic bacteria. Virulent or high number of pathogenic bacteria into the body, causing sepsis is more likely. More than 95% of urinary tract infections are caused by a single bacterium. Among them, 90% of outpatients and about 50% of hospitalized patients, the pathogenic bacteria is Escherichia coli, this bacterium serotyping up to 140 species, the urinary sensation-causing Escherichia coli and the patient’s fecal isolation of Escherichia coli belongs to the same type of bacterial type, most often seen in asymptomatic bacteriuria or urinary sensation without complications; Aspergillus, Bacillus aeruginosa, Klebsiella pneumophila, Pseudomonas aeruginosa, Streptococcus faecium, and so on, are seen in the Reinfection, indwelling catheter, there are complications of urinary tract infection; Candida albicans, new cryptococcal infections in diabetes mellitus and the use of glucocorticoids and immunosuppressive drugs in patients and renal transplantation; Staphylococcus aureus is often seen in skin trauma and drug addicts caused by bacteremia and sepsis; viruses, mycoplasma infections are rare, but in recent years there is a gradual increase in tendency. Multiple bacterial infections are seen in indwelling catheters, neurogenic bladder, stones, congenital anomalies and vaginal, intestinal and urethral fistulas.