Abstract: The experimental alloy has a nominal composition of 90W-4Ni-2Fe-4Mo (wt.%). High-purity tungsten, nickel, iron, and molybdenum powders were compacted and then subjected to liquid-phase sintering at 1460 °C for 1 h to obtain the sintered compact. Subsequently, rotary forging was performed at 850 °C with deformation amounts of 10%, 20%, and 30%. The microstructure, mechanical properties, and high-temperature softening resistance of the 90WNiFeMo alloy after different rotary forging deformation amounts were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and micro-hardness measurements. The results indicate that the rotary forging process significantly affects the mechanical properties of the alloy, particularly its strength and elongation. The sintered 90WNiFeMo alloy exhibits a micro-hardness of 298 HV, yield strength of 728.2 MPa, tensile strength of 982.2 MPa, elongation of 23.68%, and density of 17.22 g?cm?3. After 30% rotary forging, the micro-hardness, yield strength, tensile strength, elongation, and density increase to 493 HV, 1137.5 MPa, 1239.2 MPa, 0.52%, and 17.31 g?cm?3, respectively. The rotary-forged alloy exhibits higher resistance to high-temperature softening than the sintered one. Regarding fracture behavior, at small deformation amounts, the fracture mode is mainly characterized by ductile dimple fracture in the binder phase and interfacial fracture. When the deformation amount reaches 30%, transgranular cleavage fracture also appears within the alloy. As the rotary forging deformation increases, the grain size of the 90WNiFeMo alloy gradually decreases while the dislocation density increases. Dislocation strengthening and grain boundary strengthening are the main mechanisms for enhancing the yield strength of the 90WNiFeMo alloy.