Background The purpose of this study was to explore the core and driving symptoms of posttraumatic stress disorder (PTSD) of firefighters before and after rescue. Identifying core symptoms of PTSD can help clinicians to understand what may be relevant targets for treatment. Methods The study recruited 334 firefighters in a firefighter military school in September 2017 (T1). They were followed up 3 months later (T2), during which time they participated in real rescue activities. The network structure of DSM-5 PTSD was using regularized partial correlation models and a Bayesian approach computing directed acyclic graphs. Results The most central symptom both in T1 and T2 was negative emotional state. Irritable or anger emerged as a key driver of other symptoms in traumatized firefighters. Conclusions Negative emotional state and irritable or anger might represent important symptoms within PTSD symptomatology and may offer key targets in PTSD treatment for firefighters.