Objective To investigate the clinical diagnosis and treatment of fulminant type 1 diabetes mellitus (FT1DM) in pediatrcis. Methods The clinical data of children with newly diagnosed diabetes mellitus complicated with ketoacidosis (DKA) admitted to the pediatric intensive care unit from January 2015 to June 2022 were retrospectively analyzed. The subjects were divided into FT1DM group and typical type 1 diabetes mellitus (TT1DM) combined with DKA group, and the clinical characteristics and treatment of the two groups were compared. Results A total of 90 children (42 boys and 48 girls) with initial T1DM complicated with DKA were included, and the median age was 87.0 (39.0-125.0) months. There were 85 children in TT1DM combined with DKA group and 5 in FT1DM group. None of the enrolled children died or had acute pancreatitis. The onset time of children in FT1DM group was significantly shorter than that of TT1DM combined with DKA group, and the difference was statistically significant (P<0.05). FT1DM group had more significant dehydration, influenza-like symptoms, chest tightness, fatigue and lethargy, and the proportion of tachycardia and tachypnea was significantly higher than that of TT1DM combined with DKA group, and the difference was statistically significant (P<0.05). Compared with TT1DM combined with DKA group, FT1DM group had lower levels of serum sodium, glycosylated hemoglobin (HbAlc), fasting C-peptide, sodium×HbAlc, and lower positive proportions of anti-glutamic acid decarboxylase antibody (GADA) and protein tyrosine phosphatase antibody (IA-2A); serum potassium, fasting blood glucose, creatinine, blood glucose/HbAlc and potassium/HbAlc were higher in FT1DM group, and the differences were statistically significant (P<0.05). Compared with TT1DM combined with DKA group, the fluid resuscitation dose and total therapeutic dose of insulin in FT1DM group were higher and the time to correct ketosis was longer at 24/48 hours after admission, and the difference was statistically significant (P<0.05). Conclusions FT1DM is rare in pediatric patients with newly diagnosed diabetes mellitus, has a sudden onset of disease, has a more severe disorder of glucose metabolism, and can affect multiple systems. Children with FT1DM require longer treatment periods, more exogenous insulin injections, and fluid for resuscitation and expansion.