To investigate the heterogeneity of the developmental trajectory of posttraumatic stress disorder symptoms (PTS) among children and adolescents after Lushan earthquake and to explore the effect of gender and age on the trajectory.A total of 1 623 participants completed three assessments at 2 weeks, 3 months and 6 months after the earthquake. Latent growth mixture model (LGMM) was used for statistical analysis in the software Mplus 8.0.The PTS developmental trajectories among children and adolescents exposed to the earthquake had four categories: the normal stress group (31.1%, class 1), the persistent impairment group (4.5%, class 2), the psychological recovery group (46.8%, class 3) and the persistent mild symptom group (17.6%, class 4). The PTS development trajectories were significantly different in two gender groups, and the proportion of girls in the persistently injured group was higher than other three groups. The PTS development trajectories had no difference in two age groups.The developmental trajectories of PTS in children and adolescents after the earthquake have significant population heterogeneity, which is affected by gender.