Abstract: Objective To investigate the detection results and distribution characteristics of pathogenic microorganisms in bronchoalveolar lavage fluid (BALF) of children with severe pneumonia, aiming to provide a scientific basis for the precise diagnosis and treatment of such patients. Methods Children with severe pneumonia who underwent bronchoscopy with alveolar lavage and BALF sampling at the Third People's Hospital of Yancheng in 2023 were selected as subjects. The targeted next-generation sequencing (tNGS) technique was used to detect and analyze the distribution of pathogenic microorganisms in the specimens, as well as the differences across sex, age, and season. Results Among 386 BALF samples from children with severe pneumonia, Mycoplasma pneumoniae was the most frequently detected pathogen (n=324, 83.94%). There was no statistically significant difference in infection rates between male and female patients (P>0.05). However, the differences in pathogen susceptibility among different age groups were statistically significant (P<0.05): young children were more susceptible to RNA viruses and gram-negative bacteria, school-age children were more prone to Mycoplasma pneumoniae infection, and adolescents were more susceptible to gram-positive bacteria. Seasonal differences were also statistically significant (P<0.05): RNA viruses and gram-positive bacteria were more prevalent in spring, Mycoplasma pneumoniae in autumn, and DNA viruses in winter. Conclusions Mycoplasma pneumoniae is a major pathogenic microorganism causing severe pneumonia in children, with school-age children being the most susceptible group. Viruses are more active in winter and spring, making young children a key population for prevention and protection.