To investigate the incidence of myopia among rural primary school students in Bijiang District, Tongren City and analyze the effect of outdoor exercise on visual acuity during the day, a stratified sampling method was used to randomly select 1 615 primary school students aged 6～12 from 6 rural primary schools for questionnaire survey and vision screening. Among rural primary school students in this district, the average visual acuity was (4.80±0.21), and the detection rate of myopia was 27.1% lower than the domestic baseline. The mean daytime outdoor activity time (1.96±0.55) h/d of normal vision patients was more than that of myopic patients (1.68±0.52) h/d, and the difference was statistically significant (P<0.01). There was a significant difference in the frequency of outdoor activity>2 h/d during the day between the two groups (χ2=44.01, P<0.01).The results of binary logistic regression analysis showed that the risk of myopia could be reduced by 52.5%(OR=0.475, 95%CI=0.337～0.669) for each additional hour of outdoor activities during the day of the week, and the risk of myopia was reduced by 73.5%(OR=0.265, 95%CI=0.112～0.626)for more than 5 times of outdoor activity>2 h/d during the week. Increasing the time and frequency of outdoor activities during the day is a simple and effective way to prevent myopia.