Objective:To explore the application of metagenomic next-generation sequencing (mNGS) in critically ill children with hematological disorders and evaluate its diagnostic value.Methods:A retrospective analysis was conducted on the clinical data of children with hematological diseases, tumors, and hematopoietic stem cell transplantation who underwent traditional culture and mNGS testing in the pediatric intensive care unit of the Xiangya Hospital, Central South University from September 2019 to June 2022. The detection rate and diagnostic value of traditional culture and mNGS for pathogens were analyzed and compared.Results:Among the 50 patients, there were 29 males and 21 females, with a median age of 9.00(4.75-13.00) years. A total of 60 samples were sent for mNGS testing, including 40 blood samples, 10 bronchoalveolar lavage fluid samples, 7 cerebrospinal fluid samples, and 1 bone marrow, 1 skin, and 1 pleural fluid sample each. 49 positive samples were detected by mNGS, including 20 cases of viruses, 14 cases of bacteria, 8 cases of mixed samples, and 7 cases of fungi. The detection rate of mNGS in this study was significantly higher than that in traditional pathogen culture (81.7% vs 16.7%), and the difference was statistically significant ( P<0.01). Based on clinical diagnostic cases, the sensitivity of mNGS was significantly higher than that of traditional culture (85.2% vs 29.6%), with a statistically significant difference ( P<0.01), while its specificity was not statistically significant ( P>0.05) compared to traditional culture (50.0% vs 83.3%). Conclusions:mNGS has a higher detection rate and sensitivity than traditional pathogen culture, and can early identify viral, fungal, and mixed infections, providing strong assistance for precise treatment of critically ill children with hematological conditions.