To investigate the clinical characteristics of febrile infection‐related epilepsy syndrome (FIRES). We used trajectory analysis and logistic regression analysis to investigate the clinical characteristics and prognostic risk factors respectively. Twenty‐seven patients (16 males) were included. The median age of onset was 7 (IQR: 4–9) years. Routine cerebrospinal fluid (CSF) examination was normal. Electroencephalogram (EEG) showed frequent microseizures and electroseizures in all patients. Eight patients had claustrum signs in the acute phase. Anesthetics and anti‐seizure medications (ASM) were used in all patients. All patients received immunotherapy, including plasma exchange (n = 4), immunoglobulin (n = 26), and corticosteroids (n = 19). Trajectory diagrams of seizure showed 6 patients had bimodal disease course. Besides, we found there may be a linear relationship between body temperature and convulsion frequency (R2 = 0.25). The median Glasgow outcome scale (GOS) was 3 (IQR: 1–4). Nine deaths occurred, including abandonment of treatment (n = 3), hemodynamic instability (n = 3), brain hernia (n = 2), and brain hernia with hemodynamic instability (n = 1). Seizure onset combined with fever (p = 0.003), periodic discharge (p = 0.002), and non‐ketogenic diet (non‐KD) (p = 0.005) were independent risk factors for death. The KD group (n = 10) had lower mortality (p = 0.009), lower convulsion frequency at latest follow‐up (p < 0.001), less ASM (p = 0.002), and higher GOS (p < 0.001) than non‐KD group (n = 17). Therefore, some FIRES patients may have bimodal disease course. There may be a linear relationship between body temperature and convulsion frequency. Seizure onset combined with fever, periodic discharge and KD may affect the prognosis.