This study was performed to clarify the impacts of the COVID-19 pandemic on high school children's living conditions, lifestyle, living and studying habits. Cross-sectional research was conducted on 2369 high school students, selected from several high schools in Hanoi, Thanh Hoa, Thai Binh, and Dak Lak provinces. The result showed that during the COVID-19 epidemic period, living conditions were changed, such as isolation in the living area (22.1% of participants), reduced family income (35.9% of participants’ fathers and 37.3% of participants’ mothers salary decreased). Most children must switch to online learning (67.6%), and children tended to sleep later and wake up later (16.7% and 11.2%). Children tended to eat more meals and much food each meal than before. The percentage of children who spent over 3 hours\day using electronic devices increased during the COVID-19 epidemic (54.8% compared to 33.8% before). Our findings indicated that the COVID-19 pandemic had adverse effects on children's living conditions, lifestyles, and habits.