Multistage composite cermet, preparation method thereof and shield cutter

The invention provides a multistage composite cermet, which comprises a matrix phase and a plurality of granules distributed in the matrix phase; each granule comprises a wear resistant phase and an n-layer transition phase that clads the outside of the wear resistant phase, wherein, n>=1; the hardness of the n-layer transition phase reduces gradually; the hardness of the layer of the transition phase in contact with the wear resistant phase is highest; and the wear resistant phase comprises a W/Re-B-Ni3Al-Sic alloy. The W/Re-B-Ni3Al-Sic alloy is used as a superhard wear resistant phase and is in the center surrounded by the transition phase to form superhard composite cermet granules; and the composite hard alloy granules are distributed in a toughening matrix phase uniformly to obtain the multistage composite cermet that has a special structure. The multistage composite cermet has a high wear resistance and a high fracture toughness at the same time. The invention also provides a preparation method of the multistage composite cermet and a shield cutter.