Although there are an increasing number of studies that have explored the mental health consequences of COVID-19 focusing on revealing risk factors, the longitudinal research examining the potential mechanism of the co-occurrence of posttraumatic stress symptoms (PTSS) and depression symptoms among adolescents were scarce. The present study identified the important comorbidity symptoms and explored longitudinal relationship of PTSS and depression symptoms from the network perspective. A two-wave investigation (4 months interval; T1 and T2) was conducted with a sample of 1225 Chinese adolescents. Cross-sectional network and cross-lagged panel network (CLPN) analyses were adopted. Results showed that comorbidity symptoms consisted of both overlapping and non-overlapping symptoms, including “Future foreshortening” at T1 and T2 from PTSS, and “Hard to get started” at T1 and “Not sleep well” at T2 from depression symptoms. Strong longitudinal pathways appeared from all PTSS to depression symptoms, among which the pathway from “Difficulty concentrating” to “Hard to get started” was the strongest. These findings suggest that the possible comorbidity between PTSS and depression symptoms is caused by their independent and related structures, and their longitudinal association. Clinical intervention for these symptoms may alleviate adolescents’ psychological problems in the aftermath of traumatic events.