Clinical relevance In recent years, the concept of hyperopia reserve, defined as a physiological hyperopic refractive status preceding emmetropia and myopia, has gained increasing attention. and raised awareness about myopia. This concept has become of interest to both parents and practitioners. Background To report the distribution of refractive errors and ocular biometry in a large scale of preschool children in Beijing, in North China. The distribution of hyperopia reserve and its associated factors were also further investigated. Methods This study presents baseline data from Beijing Hyperopia Reserve Research (BHRR), which enrolled 2109 preschool children from 22 randomly selected kindergartens. Cycloplegic refraction was performed for all children. Hyperopia reserve was defined as a spherical equivalent refractive error (SER) greater than zero. Parents completed a questionnaire about the severity of refractive status (normal; mild myopia <-3D; moderate myopia >=-3D and <=-6D; high myopia >-6D) and their children's indoor and outdoor activity times. Results The mean SER was + 1.11 +/- 0.97D, and the mean axial length was 22.25 + 0.73 mm in all preschool children. The overall prevalence of myopia was 3.7%, with age-specific rates of 2.8%, 3.8%, 3.8%, and 5.2%, respectively. A total of 1932 children (91.6%) had hyperopia reserve, yet only 24.1% of children had age-adjusted normal hyperopia reserve. Regression analysis showed that maintaining hyperopia reserve was associated with sex (boy as reference, OR = 1.7, P = 0.005), mild myopic group parents (Father: OR = 1.7, P = 0.003; Mother: OR = 2.2, P < 0.001), increased outdoor activity time (OR = 1.3, P = 0.031) and reduced study time (OR = 0.8, P = 0.025). Conclusions The present study provided a comprehensive database on the refractive status and ocular biometry of preschool children aged 3-6 years in Beijing, North China. Although most children maintained hyperopia reserve, the majority had age-adjusted hyperopia reserve deficiencies. Early intervention, particularly for children with parents exhibiting severe myopia may be warranted.