Abstract: In order to further study the machining mechanism of ultrasonic micro-forging and the surface of the processed material， the ultrasonic micro-forging and strengthening machining of TC4 titanium alloy was taken as the research object， the semi-analytical method(SAM)based on Boussinesq solution and DC-FFT algorithm was used to establish the mathematical model of loading in the machining process and solve it， and the machining mechanism was analyzed and discussed. At the same time， the finite element model was established to analyze the complete machining process， verify the semi-analytical results， and compare it with the traditional rolling finishing machining. The results showed that the surface of ultrasonic micro-forging can form a certain depth of residual compressive stress layer and plastic deformation strengthening layer， and has better surface strengthening effect than the traditional rolling finishing strengthening.

Key words: titanium alloy; ultrasonic micro-forging; rolling finishing strengthening; semi-analytical method(SAM); finite element