<p>Tungsten heavy alloy (WHA) possesses excellent mechanical and physical properties, making them promising for use as first wall materials in the nuclear industry. Severe plastic deformation during ultrasonic elliptical vibration cutting (UEVC) changes the microstructure of the machined surface, which is closely related to its resistance to irradiation. However, the study of the microstructure formation mechanism in UEVC is still unclear, which seriously limits the application of tungsten alloy in the field of high-energy physics. To elucidate the cutting behavior and microstructural formation mechanism in UEVC, this study developed a finite element (FE) model based on a mechanism-based unified viscoplastic constitutive model. Compared to conventional cutting (CC), the ultrasonic hammering action and variable cutting speed of UEVC improve the plastic strain and strain rate. The acoustic softening effect due to high strain rates leads to high dislocation densities and small grain sizes on the machined surface. Moreover, the ultrasonic hammering effect enhances with cutting speed, which produces greater plastic strains and strain rates. This produces more severe plastic deformation, deepening the high dislocation density layer and the grain refinement layer. Finally, macroscopic morphology and microstructure revealed that UEVC-processed surfaces exhibit reduced damage, accompanied by severe dislocation entanglement and pronounced grain refinement. This study reveals the microstructure formation mechanism of UEVC, paving the way for microstructure modulation of tungsten alloy parts through machining processes.</p>