Objective To explore the diagnostic value of metagenomic next-generation sequencing (mNGS) in severe community-acquired pneumonia (CAP), and provide basis for the rational application of this technology. Methods Clinical data of 3 cases of severe CAP successfully treated in a hospital were reviewed, the role of mNGS in etiological diagnosis was analyzed, experience and procedures of rational application of mNGS were summarized based on previous literatures and self-experience. Results Bronchoalveolar lavage fluid was taken from 3 patients with severe CAP who failed in initial treatment, specimens were performed mNGS, results indicated that 3 patients were infected with Streptococcus, adenovirus type 7 and Chlamydia psittaci respectively. According to the results of mNGS, therapeutic plan was subsequently adjusted, patients' symptoms quickly relieved, and their clinical outcomes were good. Conclusion mNGS plays an important role in the rapid etiological diagnosis of severe CAP, but it is also necessary to recognize its limitation and make rational application.