To study the prevalence and risk factors of myopia in the initial stage among third-grade students in public primary schools, and to provide protective suggestions for the prevention and control of myopia among adolescents. Methods: A cross-sectional study was used. From November 2017 to February 2018, a total of 1 004 third-grade students in Gongshu District of Hangzhou City were surveyed. Myopia questionnaires were used and eyesight-related parameters were obtained using cycloplegic refraction and biometry. Detailed questions on date-of-birth, outdoor activities, indoor activity, and parental refractive errors were asked in face-to-face interviews using a standard questionnaire. Cycloplegic refraction was performed on each research subject and a spherical equivalent (SE) of≤-0.5 D was designated as the myopia group and an SE>-0.5 D was designated as the non-myopia group. A rank sum test and Chi square were applied for parameters between the myopia and non-myopia groups. A binary logistic regression analysis was performed with myopia/non-myopia as dependent variables and all parameters as independent variables. Results: The prevalence of myopia (SE≤-0.5 D) was 32.3% among the 1 004 investigated subjects, 29.2% for male students and 35.4% for female students, implying a significant difference (χ2 =4.43, P=0.035). Myopia prevalence for subjects born in the second quarter was significantly higher than those born in the first (χ2 =4.30, P=0.041) and the fourth quarters (χ2 =12.06, P<0.001). Logistic regression analysis demonstrated that the risk factors for the prevalence of myopia include degree of myopia on the paternal side (OR=1.509, P<0.001), degree of myopia on the maternal side (OR=1.360, P<0.001), female gender (binary logistic regression, OR=1.329, P=0.049), time spent on nearwork after school (OR=1.467, P=0.034), time spent on nearwork during holidays (OR=1.352, P<0.001), time spent on middle-distance work after school (OR=1.626, P=0.045) and time spent on middle-distance work during holidays (OR=1.860, P<0.001), while time spent outdoors after school (OR=0.618, P<0.001) and time spent outdoors during holidays (OR=0.823, P=0.004) act as protective factors. Conclusion: For the initial stage of myopia, our data analysis on third-grade students in the Gongshu District of Hangzhou shows that less outdoor activity, more near-distance and middle-distance work, parental history of myopia and female gender were associated with a greater risk for myopia. More outdoor activities may help to reduce the high prevalence of myopia. In addition to school days, holidays deserve more attention.