BackgroundMost research has suggested that children and adolescents had poorer mental health than pre-COVID-19 pandemic status. There have been few investigations into factors associated with pre-peri pandemic differences in young people’s mental health status. Our study aimed to investigate the association between sociodemographic factors, attitudes, and daily life experiences and these differences.MethodsWe used self-reported cross-sectional data from the Youth Sexuality Survey (YSS) by the Family Planning Association of Hong Kong, collected from secondary school students aged 10–16 between the fourth and fifth waves of the pandemic. The study outcome was pre-peri pandemic differences in mental health (better, unchanged, or poorer). Associations between the study outcome with age, sex, satisfaction with academic performance, school life, relationship with classmates and family life, and average sleeping and exercising time in the past month, were assessed through multinomial logistic regression, controlling for depressive/anxiety symptoms and change in physical health status since the pandemic.ResultsThere were 6,665 respondents. Compared with pre-pandemic, approximately 30% reported poorer mental health, whilst 20% reported better mental health. Females (OR = 1.355, 95% CI = 1.159–1.585) and those dissatisfied with their academic performance (OR = 1.468, 95% CI = 1.233–1.748) were significantly more likely to report poorer mental health with reference to unchanged status, while those satisfied with family life had improved mental health with reference to unchanged (OR = 1.261, 95% CI = 1.006–1.579) and poorer status (OR = 1.369, 95% CI = 1.085–1.728).ConclusionPolicy and community strategies that promote good family relationships are thus essential for young people’s mental health during societal challenges such as the COVID-19 pandemic.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13034-023-00622-x.