〔Abstract〕 Objective In this study, we detected angiotensin-converting enzyme 2(ACE2) and transmembrane protease, serine 2(TMPRSS2) expression of different ages(newborn, juvenile stage, adulthood and aged mice) and different tissues(lung, heart and small intestine) in mice to reveal the potential age and target organ that were susceptible to corona virus disease 2019(COVID-19) infection. Methods The conservatism of TMPRSS2 and ACE2 among different species was analyzed by online bioinformatics analysis website(Uniprot). Real-time Quantitative PCR was used to analyze relative expression of ACE2 and TMPRSS2 mRNA at different ages and different tissues in mice. Western blot was used to analyze relative expression of ACE2 and TMPRSS2 protein at different ages and different tissues in mice. Results (1)The homology of ACE2 between human and mice was 82.1%, and the homology of TMPRSS2 was 78.4%;(2)Compared with 1-3 day old(newborn group) mice, the expression levels of ACE2 and TMPRSS2 mRNA in lung and small intestine tissues of 1-month old(young group), 3-month old(adult group) and 18-month old(old group) mice increased(P<0.05); compared with newborn mice, ACE2 and TMPRSS2 mRNA expression in heart tissues of young and adult mice increased(P<0.05), and TMPRSS2 and ACE2 mRNA expression in elderly group decreased(P<0.05);(3)Differences in ACE2 and TMPRSS2 mRNA expression levels in different tissues of mice of the same age group were statistically significant, and the highest expression levels were in lung tissue(P<0.05);(4)The tendency of ACE2 and TMPRSS2 protein and gene expression was consistent. Conclusion With the increase of age, the expression of ACE2 and TMPRSS2 in lung and small intestine of mice also increased, which may mean that advanced age is one of the independent risk factors for infection of Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV-2) in mice and even humans. In addition, the high expression of ACE2 and TMPRSS2 in the lung tissue of the same age mice group may suggest that the lung is the main target organ for SARS-CoV-2 invasion.