Few studies have examined the psychological impact on adolescents of family confinement and infection exposure during the COVID-19 pandemic. However, these surveys lacked follow-up data to determine how the family confinement affects participants' depression and anxiety. The purpose of this study was to evaluate the psychological status and related risk and protective factors of adolescents after two months of family confinement for preventing COVID-19 in China, and compare them with baseline data. We surveyed teenagers in January 2020 before the COVID-19 outbreak (T1) and after home confinement (T2). We used the Patient Health Questionnaire (PHQ), the Generalized Anxiety Disorder (GAD) Scale and the Childhood Trauma Questionnaire (CTQ). 13,637 valid questionnaires were collected at T1, of which 22.34% reported depressive symptoms (PHQ-9 >= 10) and 14.42% reported anxiety symptoms (GAD-7 >= 10). At T2, the rates decreased to 14.86 and 7.44%, respectively (all P < 0.0001). Of the adolescents, 223 reported potential risk of exposure to COVID-19. We then compared them to the 9639 non-risk adolescents using a propensity score matching analysis. The adolescents with potential exposure risk had higher rates of depression (26.91 vs 15.32%, P = 0.0035) and anxiety (14.80 vs 7.21%, P = 0.01) than risk-free adolescents. Among adolescents with an exposure risk, psychological resilience was protective in preventing depression and anxiety symptoms, while emotional abuse, a poor parent-child relationship were risk factors. Long-term home confinement had minimal psychological impact on adolescents, but COVID-19 infection rates accounted for 50% of the variance in depression and anxiety among adolescents even with low community rates.