Myopia has become one of the top three public health problems in our schools? and it is the most difficult to control. Myopia-induced fundus lesions and even macular degeneration are important causes of disabling eye disease and monocular blindness. Preventing the onset and progression of myopia is an issue that requires the combined efforts of health, society, schools and families. Studies have shown that cumulative outdoor activity of 20 hours per week is effective in controlling the onset and progression of myopia. Note that the emphasis here is on outdoor rather than activity. The mechanism of outdoor activities to control myopia: 1. In the outdoor environment, most objects are at a distance and the human eye does not need to adjust, so there is no adjustment lag. Adjustment lag is one of the mechanisms that produce myopia. 2, outdoor environment, sufficient light, pupil narrowing, depth of field increases, good retinal imaging quality, good retinal imaging quality can delay myopia deepening. 3, sunlight action, the retinal tissue produces a variety of neurotransmitters, such as dopamine, vitamin D, etc. These substances are believed to protect the development of myopia in the eye. 4. In outdoor environments, most objects are in myopic defocus in the eye, and myopic defocus is thought to retard eye elongation. In light of this research, experts recommend that: 1. students should be encouraged to go outdoors during school recess; 2. physical education classes should be routinely held outdoors; 3. balancing hygiene habits with study habits. Students should participate in active outdoor activities after school to ensure that they have one hour of outdoor activity after school.