The present disclosure relates to a JAK inhibitor upadacitinib intermediate and a preparation method therefor, and to a preparation method for a JAK inhibitor upadacitinib. The upadacitinib intermediate of the present application is as shown in Formula (II) or Formula (III),






wherein, R is a protective group of nitrogen atoms, and R1 is an open-chain or cyclic amine group. Compared with the prior art, the method for the synthesis of upadacitinib of the present application, significantly reduces cost, is environmentally-friendly. And the quality of the final product is well controlled.