In the post-pandemic era, psychological traumas have emerged as major mental health issues. However, the post-traumatic reactions and their connections with social-emotional competence among high school students experiencing COVID-19 lockdown have not been adequately explored. This study aimed to reveal the characteristics of their positive and negative post-traumatic reactions, and their connections with social-emotional competence. Network analysis was used on data from 1096 Chinese high school students who experienced COVID-19 lockdown. Measures included the DSECS-S, the PTGI and the PC-PTSD-5. The results revealed that “Valuing life” and “Recalling unwillingly” were identified as core factors of post-traumatic reactions, while “Having close friendships”, “Getting along well with others” and “Respecting others’ emotions” played a bridging role in connecting the communities of social-emotional competence and post-traumatic reactions. This study enriches research on post-traumatic reactions, emphasizing the importance of implementing social-emotional competence programs to tackle mental health crises.