Out-of-school life is a vital part of a kid’s life. And a reasonable organization of children’s out-of-school life plays an important role in the comprehensive development of their morality，knowledge，physical strength，aesthetic standard and labor skills. This paper adopts the self-compiled Out-of-school Life Time Usage Table to investigate on children’s time usage and its relation with their development at different periods in kindergarten，primary school and junior middle school. It has three discoveries：First，homework takes up much of students’ out-of-school time on weekdays，but they still have leisure time to play or do sports；while on weekends，outdoor activities almost take the same amount of time as doing homework. However，electronic devices now take up increasingly more time. Second，there are different characteristics of out-of-school time usage considering children’s gender，stage of schooling，annual family income，parent’s ideas towards education，and their urban or rural identities. Third，there is a significant correlation between children’s out-of-school time usage and their physical development，creativity，social skills，and resilience. Therefore，the paper gives some concrete recommendations to improve the quality of children’s out-of-school life.