ObjectivesTo ascertain the prevalence and associated factors of anxiety symptoms among middle and high school students in Zhejiang after 2 years of the COVID-19 pandemic.DesignA school-based cross-sectional study.Setting30 counties/districts in Zhejiang Province, China.Participants27 019 students attending middle and high schools.Outcome measuresAnxiety symptoms were assessed using the Generalised Anxiety Disorder 7-item scale (GAD-7). A total score of 10 or more is considered indicative of anxiety symptoms.ResultsThe overall prevalence (95% CI) of anxiety symptoms was 14.2% (13.4 to 15.0), higher among girls (18.6%, 95% CI: 17.5 to 19.7) than boys (10.2%, 95% CI: 9.5 to 10.9) (p<0.001), higher among rural students (15.1%, 95% CI: 14.1 to 16.2) than urban students (12.5%, 95% CI: 11.6 to 13.4) (p<0.001). Older age (14–15 years, OR=1.25, 95% CI: 1.09 to 1.44; ≥16 years, OR=1.32, 95% CI: 1.07 to 1.63), being girls (OR=1.76, 95% CI: 1.58 to 1.96), living in rural areas (OR=1.14, 95%CI: 1.01 to 1.29), poor academic performance (OR=1.20, 95% CI: 1.03 to 1.41), alcohol drinking (OR=1.15, 95% CI: 1.01 to 1.30), inadequate fruits (OR=1.31, 95% CI: 1.19 to 1.45) and vegetables intake (OR=1.32, 95% CI: 1.10 to 1.57), insomnia (sometimes, OR=2.14, 95% CI: 1.93 to 2.38; often/always, OR=4.73, 95% CI: 4.03 to 5.56), loneliness (sometimes, OR=2.97, 95%CI: 2.59 to 3.41; often/always, OR=8.35, 95% CI: 7.20 to 9.69), sadness (OR=2.51, 95% CI: 2.25 to 2.79) and physical fight (OR=1.29, 95% CI: 1.13 to 1.48) were positively associated with anxiety symptoms, while studying at vocational high school (OR=0.61, 95% CI: 0.49 to 0.75), coming from family with middle income (OR=0.76, 95% CI: 0.64 to 0.89), being physically active 3–7 days weekly (OR=0.85, 95% CI: 0.75 to 0.95) were negatively associated with anxiety symptoms.ConclusionAnxiety symptoms prevailed among middle and high school students in China. A variety of factors, containing sociodemographic factors, lifestyle behaviours, mental health, academic performance and physical fight should be taken in consideration in addressing prevention and intervention of anxiety symptoms.