AIM: To know the rate of students' myopia in junior school and factors affecting its occurrence in high altitude Tibetan areas in Qinghai, and provide basis for the prevention of myopia.

METHODS: Totally 2 209 junior school students were extracted as respondent with stratified cluster sampling method. The gender, age, ethnicity, grade, eye behavior, physical activity and parental visual conditions were collected by self-made questionnaire, and the curvature of the cornea, anterior chamber depth and axial length were detected.

RESULTS: The prevalence of myopia was 48.02%, including the mild myopia, moderate myopia and high myopia were 40.74%, 35.31% and 23.96% respectively. Curvature of the cornea, anterior chamber depth and axial length had statistical difference between normal vision and different degrees of myopia(P<0.05). The prevalence of myopia had statistical difference in different gender, ethnicity, grade, visual near distance, sitting posture, eye exercises, outdoor activity time each week and the case of parents eyesight(P<0.05). Gender, ethnicity, grade, visual close range, sitting posture, eye exercises, outdoor activity time each week and the case of parents eyesight were the factors affecting the occurrence of myopia by using logistic regression analysis.

CONCLUSION: Incorrect sitting posture, parental myopia, visual near distance <20cm, incorrect eye exercises and less time for outdoor activities are the main reasons that cause myopia of junior students. The effective prevention and controlled measures should be taken for these factors.