Regular vacation is known as menstruation. There are many reasons why a 13-year-old girl does not have her period for six months, which may be due to the imperfect development of the neuroendocrine system, excessive pressure from studies and other reasons. It is recommended to consult a doctor in time to find out the cause and under the guidance of the doctor for observation or medication. 1. Imperfect development: may be due to the hypothalamus – pituitary – ovary function is not well developed, resulting in unstable menstrual cycle and other symptoms, at this time the patient does not need to worry too much, with the growth of age, the patient’s symptoms will gradually disappear. 2. Too much pressure from studying: due to excessive pressure from studying or irregular work and rest, the hormone secretion in the patient’s body is unstable, which may lead to unstable menstrual cycle and other problems. There may also be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.