Infectious diseases remain leading causes of mortality and morbidity in children. Rapid and accurate diagnosis of infectious diseases in children is important for developing an effective treatment and management strategy. However, the current diagnosis of infectious agents mainly depends on culture and molecular testing. Both of the methods either has long turnaround times or narrow detection range. Metagenome next generation sequencing (mNGS) has been applied to the diagnosis of central nervous system infection, lower respiratory tract infection and sepsis, which showed high positive rate, short turnaround time. However, there is currently no assessment of the diagnostic efficacy of mNGS in children infectious diseases. This study used the DNA extraction and library construction technology developed for children's low volume clinical samples to assess the sensitivity and specificity of mNGS in the diagnosis of infectious diseases, and the treatment outcome based on mNGS test results.