9 years old girl to menstruation is not normal, girls should normally be 11 years old breast development, 13-13.5 years old to menstruation, 9 years old to menstruation belongs to the early sexual development too much, will cause two effects on the child: First, the child’s adult lifetime height is too short, once menstruation is not much room for growth; Second, because of premature sexual development will lead to abnormalities in the child’s psychological behavior, will lead to psychological diseases. Once a girl gets her period at the age of 9, she should be taken to the hospital for a bone age check to determine the remaining room for growth and whether her height needs intervention. Blood hormone tests and ultrasound tests of the uterus, ovaries and sexual organs should also be done to comprehensively evaluate the severity of the child’s precocious puberty and early sexual development and provide treatment as soon as possible.