A class of ketoamide-based compounds, in particular, a ketoarnide-based compound as represented by general formula A is provided. The ketoamide compound may be used as a 2019 novel coronavirus (2019-nCov) 3 CL protease inhibitor and/or human cathepsin L inhibitor, and/or may be used in the preparation of a medicament for treating and/or preventing and relieving respiratory tract infection, pneumonia and other related diseases caused by 2019 novel coronavirus infection. Pharmaceutical compositions of the class of compounds, pharmaceutical salts, enantiomeric forms, diastereoisomers and racemic compounds thereof in the preparation of a medicament for treating and/or preventing and relieving respiratory tract infections and other related diseases caused by the 2019 novel coronavirus infection are also provided.