Acute cystitis is an acute infectious disease of the urinary system caused by infection of the bladder mucosa with pathogenic microorganisms such as Escherichia coli, Streptococcus, Staphylococcus aureus, etc. It is mostly seen in newly married female patients and is mainly caused by retrograde infection of bacteria from the urethra. The main clinical manifestations are urinary frequency, urinary urgency, urinary pain, hematuria, small abdominal pain, chills and fever. Acute cystitis is mostly caused by bacterial infection and is commonly seen in women, mainly due to the anatomical structure of the female reproductive system. The female urethra is short, wide and straight, and is close to the opening of the vagina, so during sex or in case of vaginitis, bacteria can easily enter the urethra and bladder retrograde through the urethra and cause cystitis, resulting in congestion and edema of the bladder mucosa, and in severe cases, ulceration of the bladder mucosa, resulting in pus and hematuria. This can lead to pus and hematuria. If bacteria enter the blood system, they can cause high fever and chills. In addition, certain medical procedures can cause acute cystitis, such as cystourethroscopy and catheterization. In summary, acute cystitis is caused by bacteria entering the bladder retrograde from the urethra, and is directly related to impure sex and vaginitis.