The invention discloses an application of an interferon regulatory factor 5(IRF5) and an inhibitor thereof in treating cardiac hypertrophy, and belongs to the filed of function and application of genes. The application of the interferon regulatory factor 5(IRF5) and the inhibitor thereof in treating cardiac hypertrophy determines the relationships between the expression of IRF5 genes and cardiac hypertrophy disease. The relationships are inhibiting the expression of the IRF5 genes, accordingly remarkably inhibiting cardiac hypertrophy and fibrosis, and improving cardiac function; promoting the expression of the IRF5 genes, accordingly remarkably promoting cardiac hypertrophy and fibrosis, and deteriorating cardiac function. Thereby, IRF5 can be adopted as a drug target used for screening drugs which protect cardiac function, prevent, relieve and/or treat cardiac hypertrophy and resist myocardial fibrosis. The inhibitor of IRF5 can be used for preparing drugs which protect cardiac function, prevent, relieve and/or treat cardiac hypertrophy and resist myocardial fibrosis.