Objective To explore the application value of metagenomic next-generation sequencing (mNGS) based on human sequencing in the clinical early diagnosis of lung cancer. Methods Four patients hospitalized with suspected lung infection were retrospectively analyzed, and the test results of bronchoalveolar lavage fluid (BALF) on mNGS of tumor metagenome, the routine clinical test results, and their clinical diagnosis and treatment information in between August 26, 2021, and December 18, 2021. Results Patient 1 was preliminarily diagnosed with lung cancer by referring to chest computed tomography (CT) imaging. Chest radiograph or CT in the other three patients showed bilateral lung CT and lamellar hyperintensities (patient 2), bilateral lung mass-like and lamellar hyperintensities (patient 3), and lung masses (patient 4), respectively. BALF samples from all 4 patients were detected with mNGS based on human tumor sequences, indicating tumor. In addition, the result in patient 3 also indicated white pseudofilamentous yeast infection consistent with clinical culture, and the result in patient 4 also showed infection of rhinovirus type A. Conclusion The second generation genome sequencing technology based on human sequence can not only assist clinical diagnosis of infection, but also provide detection datUM support for tumor early warning.