Frequent urination of three-year-old babies may be caused by physiological factors, polyuria, inflammatory urinary frequency, neurogenic urinary frequency, reduced bladder capacity urinary frequency, periurethral lesions and other reasons. 1. Physiological factors: for example, drinking more drinks or water, mental stress, cold environment, can lead to increased urination, which is mostly normal. Reducing fluid intake, improving the environment and adjusting the mood can usually improve the situation of frequent urination. 2. Pathologic factors: (1) polyuria urinary frequency: the number of times of urination increased, and each time the volume of urine is not less, and the total volume of urine increased. See diabetes mellitus, uremia, etc. (2) Inflammatory urinary frequency: frequent urination and each time the volume of urine is less, mostly accompanied by urinary urgency, urinary pain, such as cystitis, urethritis, prepuce and glans penis. (3) Neurogenic urinary frequency: frequent urination and small amount of urine each time, mostly seen in central and peripheral neuropathy, such as neurogenic bladder. (4) Reduced bladder capacity urinary frequency: such as bladder occupation, bladder tuberculosis, etc., manifested as persistent urinary frequency. (5) Periurethral lesions: urethral polyps, parurethral cysts, etc. irritation of the urethral orifice causing frequent urination. There are many causes of frequent urination in three-year-old babies, and parents are advised to bring their children to regular hospitals for relevant examinations and active treatment.