The selective inhibition for JAK2 over the other JAK family kinases(JAK1,JAK3 and TYK2),avoiding the side effects effectively,has shared an immense challenge due to the high conservatism.In this paper,the highly JAK2 selective mechanism of the thienopyridine derivative 19 was identified at the molecular level,based on the insights into the inhibitory effects of the compound 19 on four JAK kinases by molecular docking,molecular dynamic simulations,free energy calculation and decomposition.