The invention discloses an application of a quinolinone compound as an hCBS (human cystathionine beta-synthase) enzyme inhibitor, and particularly relates to the application of the compound 7-amino-2-hydroxy-5-imino-6,7-dihydroquinolin-8(5H)-one as the hCBS enzyme inhibitor. The small-molecular compound is the 5,7-diamino quinolinone compound, has the IC50 on an in-vitro hCBS enzyme-catalyzed reaction of 4 [mu]M, and can be used as a tool drug for study on an H2S signal channel and a lead compound for development of drugs for treating circulatory shock, stroke, Down syndrome, tumor and other diseases related with H2S.