The goal of this multi-center, randomized, parallel-controlled clinical trial is to evaluate the effectiveness of outdoor activities monitoring and motivating by smartwatches to prevent myopia progression in children. The main question it aims to answer are:

1. To evaluate the two-year change of spherical equivalent progression.
2. To evaluate the change in axial length, the incidence of myopia, the time of outdoor activity, the choroid thickness, and blood flow through the two-year intervention.

Participants will wear smartwatches and receive Mini Program outdoor activity reminders and motivations. The required outdoor activity time is 2 hours from Monday to Friday and more than 2 hours on weekends. The control group will only wear smartwatches for monitoring. Researchers will compare the control group and the intervention group to see if outdoor activities can protect myopia or not.

Inclusion Criteria:

1. Gender is not limited;
2. Age: 4 ~ 9 years old;
3. Spherical equivalent: -0.5D < SE < 2.5D;
4. Be able to follow up for at least 2 years;
5. Be able to wear a smartwatch on a daily basis as required;
6. Parents or guardians sign an informed consent form;
7. Children over 6 years old need oral consent to participate.

Exclusion Criteria:

1. Anisometropia > 1.50D;
2. Using other interventions for controlling myopia including atropine, rigid orthokeratology lenses, bifocal lenses or progressive lenses, red light, acupuncture, etc.;
3. Strabismus and/or amblyopia;
4. Previous history of eye surgery (including strabismus correction);
5. Ocular or systemic diseases that may be related to the development of myopia or myopia: such as Marfan syndrome, neonatal retinopathy, diabetes, etc.;
6. Other circumstances that the investigator judges inappropriate to participate in the trial.