With the development of statistical methods and the emergence of individual-centered research perspective, studies on the impacts of some natural/factitious disasters have verified the group heterogeneity manifested in the development of post-traumatic stress symptoms (PTSS) of adolescents after those disasters. Whereas, the PTSS of adolescents after major public health emergencies is still rarely explored. The study discusses the development trajectories and characteristics of the PTSS of adolescents during the COVID-19 pandemic, and explores the factors accounting for different trajectories of PTSS of adolescents, so as to provide theoretical basis for post-disaster psychological assistance. This study conducted a one-year tracing survey since the second month after the outbreak of the COVID-19 pandemic, and tracked 820 students in a middle school in Hubei Province. These students all experienced home quarantine in Hubei at the initial stage of the pandemic. The follow-up survey was conducted 4 times, individually in the second month, the forth month, the seventh month, and the thirteenth month after the outbreak. In the first survey, trauma exposure and demographic variables were measured. In each survey, the PTSS was measured. The study adopted a mixed growth model of latent variables to classify the development trajectory of adolescents’ PTSS, and used multiple logistic regressions to test the influencing factors accounting for different trajectories of PTSS of adolescents. The study shows an overall downward trend of the PTSS of adolescents showed within the year after the pandemic. The study finds three types of development trajectories of the PTSS: resilient (84.1%), relapsing (8.2%) and recovery (7.7%). Grade, degree of trauma exposure, negatively emotional events after the outbreak, and whether depression and anxiety were detected at the beginning of the outbreak were important factors for the development of PTSS. There is individual heterogeneity in post-traumatic stress symptoms. Adolescents of higher grades, with higher levels of trauma exposure and with obvious negative emotions early in the disaster and excessive negatively emotional events after the disaster tend to show malignant development trajectories of PTSS. Schools and the whole society need to pay long-term attention to and give appropriate psychological support to adolescent group with these mentioned characteristics.