Objective To investigate the expression of angiotensin-converting enzyme 2 (ACE2) (a receptor of severe acute respiratory syndrome coronavirus 2[SARS-CoV-2]) in human lung and its significance in SARS-CoV-2 infection. Methods Genotype-Tissue Expression (GTEx) database was used to analyze the gene transcription levels of ACE2 in human normal tissues and organs. Immunohistochemistry was used to detect the protein expression levels of ACE2 in different anatomical sites of primary human lung tissues. Results The expression levels of ACE2 gene and protein in human lung were low, which were mainly expressed in a small number of type Ⅱ alveolar epithelial cells in alveolar tissue, but not in vascular endothelial tissue, bronchial, bronchiole, terminal bronchiole, respiratory bronchiole, or other bronchial tissues. Conclusion The expression of ACE2 in human lung is quite low, and is mainly located in a small number of type Ⅱ alveolar epithelial cells, indicating that human lung possesses the molecular basis for ACE2 to cause SARS-CoV-2 infection, and SARS-CoV-2 may have other mechanisms of infection in human lung.