The application of metagenomic second-generation sequencing (mNGS) is shifting from research to clinical laboratories due to rapid technological advances and significant cost reductions. Although many studies and case reports have confirmed that the success of mNGS in improving the prevention, diagnosis, treatment and tracking of infectious diseases, there are still some obstacles that must be overcome. The results of mNGS show all the possible pathogens in the sample, however, in the face of thousands of microbes that can infect humans, it remains challenging to accurately identify the key pathogens. So far, there is no unified interpretation standard for mNGS in clinical practice. This article reviews the interpretation of mNGS results for pathogen infection in different systems, the clinical interpretation and application regulations of mNGS results, and the challenges of mNGS interpretation in pathogen diagnosis.