Abstract: Objective To examine differences in vision,axial length/mean corneal radius(AL/CR) ratio among primary students of different grade and gender,and to identify the key population with myopia development for monitoring.Methods With random cluster sampling method,1 538 primary students in grade one and four from 6 primary schools in Yangfangdian zone of Beijing were followed-up for measures of vision and biological indicators of eyeball for three years.Results There were significant differences(P<0.01)in vision and axial ratio between primary students from grade one and grade four.and the differences changed with age increment.The prevalence of poor vision for the students of grade one was 25.5%,38.7%,and 47.3% and that of grade four was 49.3%,69.3%,and 74.3%,respectively,from 2009 to 2011.Myopia prevalence of female students was higher than that of male in the same grade.Myopia developed most progressively in the duration of grade one and two,and grade four and five,with the increasing rates of 20.0% and 13.2%.There was no significant gender difference in the vision for the students in grade one,but there was a significant difference in AL/CR ratio (P<0.05).There was a significant gender difference in vision for the students in grade four(P<0.05).Conclusion Poor vision prevalence in primary students increases with age increment,with the decline of vision level and the ascent of AL/CR.Ages of 6-7 and 10-11 are important monitoring durations for myopia prevention and control.