Objective To investigate the clinical characteristics of severe pertussis in children. Methods Clinical data of 55 children with severe pertussis and admitted to the pediatric intensive care unit (PICU) of Maternal and Child Heath Hospital of Hubei Province from January 2022 to May 2024 were retrospectively analyzed. Patients were grouped according to age (≤3-month group and ＞3-month group), vaccination status, and mixed infection status, differences in clinical characteristics among different groups of pediatric patients were compared. Results 55 children with severe pertussis were aged 1 month and 5 days-9 years, all had severe pneumonia, 54 children were improved and discharged from hospital, 1 died. 26 children (47.3%) were aged ＜3 months, 45 children (81.8%) were unvaccinated, and 47 children (85.5%) had mixed infection. The rates of post-vomiting cough and blood exchange transfusion in children in ≤3-month group were lower those in ＞3-month group (30.8% vs 58.6%; 11.5% vs 34.5%, respectively); The rate of elevation of cerebrospinal fluid protein in children in ≤3-month group was higher than that in ＞3-month group (61.5% vs 31.0%); The pre-admission disease course of children in ≤3-month group was shorter than that in ＞3-month group (［10.15±5.64］ days vs ［14.24±8.90］ days), differences were all statistically significant (all P≤0.05). The absolute counts of lymphocyte in the vaccinated group was lower than that in the unvaccinated group (［9.92±5.92］×10⁹/L vs ［17.93±11.41］×10⁹/L, P＜0.05). The usage rate of gamma-globulin in children in the mixed infection group was higher than that in the simple infection group (87.2% vs 50.0%). The length of hospital stay (［15.11±6.53］ days vs ［9.50±4.69］ days), length of PICU stay (［10.53±5.26］ days vs ［5.88±4.16］ days), and macrolides antibiotic use days (［8.36±4.21］ days vs ［5.00±2.73］ days) in children in the mixed infection group were all longer than those in the simple infection group, differences were all statistically significant (all P<0.05). No independent influencing factors were found to prolong the length of PICU stay in children with severe pertussis. Conclusion Severe pertussis mostly occurs in unvaccinated children aged ≤3 months, with a high incidence of mixed infection, all presenting as severe pneumonia. Vaccination status, mixed infection, and complications are key factors affecting prognosis.