Ultrafine-grained PM superalloy billet with approximate grain size of 3 μm was prepared by multiple forging under the near isothermal condition of 1130 oC deformation temperature and 1000 oC mould temperature, and the yield strengths at room temperature and 750 oC reach 1470 MPa and 1140 MPa, respectively. Otherwise, the microstructure evolution was observed by OM, SEM and TEM. The results indicate that the full refinement of the PM superalloy is directly caused by the entire recrystallization of many times resulting from great accumulative deformation of multiple forging. Compared with HIPed original material, the ultrafine-grained PM superalloy possesses fine tertiary γ' phases dispersed in the matrix, cleaner and thinner boundary, which present less defects such as micropores.