Abstract:Abstract: OBJECTIVE To investigate the refraction and to examine the prevalence of refractive errors in preschool children aged 3 to 6 years in Yangpu district, Shanghai. METHODS A school-based cross-sectional study was conducted in Yangpu district of Shanghai from 2018 to 2019. It randomly selected 2 419 preschool children aged 3 to 6 years old. RESULTS The mean SE in the right eye of preschool children aged 3, 4, 5 and 6 years old were (1.31 ± 0.84) D, (1.30 ± 0.76) D, (1.17 ± 0.84) D and (1.06 ± 0.80) D, respectively, and the mean SE in the right eye decreased with age. The children underwent comprehensive eye examina⁃ tions, including cycloplegic refraction measurements. The mean SE for 3 to 6 years old children in Yangpu district was(1.22±0.81)D. The main refractive state was mild hyperopia (75.53%), and the prevalence of myopia was low (2.32%). The prevalence of myopia gradually increased with age. The prevalence of hyperopia and astigmatism was 13.23% and 19.39%, respectively. The prevalence of hyperopia and astigmatism decreased gradually with the increase of age. CONCLUSION Preschool children aged 3 to 6 years in Yang⁃ pu district of Shanghai were mostly mildly hyperopic, with a low prevalence of myopia. But the average SE and refractive errors were different among all age groups. The changes of preschool children's refractive development are obvious, so it is necessary to strength⁃ en the dynamic monitoring of the refractive state of preschool children at all ages in Yangpu district, and timely detect preschool my⁃ opia and the premature end of emmetropia.