Inhalation of droplets through coughing, sneezing, or even talking can induce direct transmission of SARS-CoV-2 from person to person, and contact with the nose, eyes, and oral mucosa can also cause transmission. Compared with nasopharyngeal specimens, the matching rate of saliva to respiratory viruses (including Coronavirus) is as high as 90%. Coronavirus is only found in the saliva of some individuals but not in nasopharyngeal inhalation. Viruses come from many sources: saliva, nasopharyngeal secretions, and respiratory secretions. The goal of this study is to figure out what the molecular mechanism of SARS-CoV-2 infection through saliva is. This study was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. In SARS-CoV-2, the glycoprotein found in the viral envelope spikes binds to cell receptors in the form of ACE2. SARS-CoV-2 infection of the salivary glands is a potential since ACE2 is expressed in the salivary glands. Saliva also contains IgA, which can be used as a biomarker for high-risk patients. SARS-CoV-2 infection is detected using IgA, IgM, and IgG antibodies. Saliva samples are also more sensitive than nasopharyngeal swabs. The combined use of saliva samples and nasopharyngeal swabs is also conducive to a more accurate diagnosis. The probable molecular mechanism of SARS-CoV-2 infection from saliva may be deduced from the above statement.