A 9 year old child with 300 degrees of myopia should first find out whether it is true myopia or pseudomyopia. True myopia can be corrected by wearing frames and using keratoplasty lenses, while pseudomyopia can be treated by improving eye habits and relieving visual fatigue. Myopia can be categorized into two different types: true myopia and pseudomyopia, with very different treatments. True myopia can only be corrected because it is irreversible, and can be corrected by wearing framed glasses or using corneal reshaping lenses, which also have the effect of slowing down the growth of myopia. Pseudomyopia is caused by visual fatigue, which is reversible myopia. As long as we can pay attention to reasonable eye use and relieve visual fatigue, pseudomyopia can be eliminated naturally. Patients need to go to the ophthalmology department of the hospital as soon as possible after a detailed examination to confirm the diagnosis, and then the doctor will formulate a scientific and reasonable treatment plan to intervene.