The invention relates to the field of medicines, discloses application of 5,6,7,4'-tetrahydroxyflavone and derivatives thereof as a JAK tyrosine protein kinase inhibitor, and especially relates to application of 5,6,7,4'-tetrahydroxyflavone and derivatives thereof as a JAK tyrosine protein kinase inhibitor in preparing medicines for treating diseases related to JAK / STAT signal transduction pathway abnormity. The 5,6,7,4'-tetrahydroxyflavone and derivatives thereof provided in the invention have a strong inhibition effect on JAK tyrosine protein kinase and an enzymological binding characteristic of competitive inhibition; the 5,6,7,4'-tetrahydroxyflavone and derivatives thereof further can penetrate cell membranes and effectively intercept activation of a JAK / STAT signal transduction pathway, thereby inhibiting lymphocytes from secreting cytokines such as interferon to peripheral tissue. According to pharmacological research, the 5,6,7,4'-tetrahydroxyflavone and derivatives thereof have an obvious effect in relaxing vessels; therefore, it is indicated that the 5,6,7,4'-tetrahydroxyflavone and derivatives thereof have a critical clinical application value.