Posttraumatic stress disorder (PTSD) is prevalent among adolescents following natural disasters, and the trauma experiences represent a critical risk factor for PTSD. Nevertheless, the underlying mechanism of adolescents' PTSD following trauma experiences remains unclear. Rumination appears to be a mediating factor between trauma experiences and PTSD, and social support may moderate this mediating relationship between trauma experiences, rumination, and PTSD, but few studies have examined these assumptions. Thus, this study aimed to assess the mediating role of rumination and the moderating role of social support in the relationship between rainstorm-related experiences and PTSD among adolescents, following a rainstorm in China. Nine hundred and fifty-one middle school students completed self-report questionnaires, and structural equation modeling was conducted to examine the potential moderated mediation effect. Rainstorm-related experiences had a direct and positive effect on PTSD, and also indirectly influenced PTSD via rumination. Moreover, social support work to buffer the direct effect of rainstorm-related experiences on PTSD, but not the effect of rumination on PTSD. Implications for clinical practice and research are discussed along with study limitations.