TC4 titanium alloy is a frequently processed material in aerospace field.Due to its difficult cutting characteristics,it is usually processed by electrical discharge machining (EDM),but there are problems in processing efficiency and debris removal.Longitudinal torsional ultrasonic vibration can effectively optimize the above disadvantages,but there is no rigorous quantitative scientific analysis to prove the optimization degree of the longitudinal torsional ultrasonic vibration assistance on EDM.Therefore,a discharge energy model of longitudinal torsional ultrasonic vibration assisted EDM was proposed to explain the discharge mechanism and the influencing factors of discharge energy.Single factor experiment and orthogonal experiment were set up to explore the influence of longitudinal torsional ultrasonic vibration on EDM by significance T test.Grey relational analysis model was established to analyze the influence weight of electrical parameters and the optimal parameter array was selected.Finally,the correctness of the optimal results was verified by hole processing experiment.The results show that the peak current and pulse width have obvious effects on the machining efficiency and quality.The introduction of longitudinal torsional ultrasonic vibration significantly improves the machining performance of EDM.The optimal peak current is increased from 2 A to 3 A,and the pulse width is increased from 125 μs to 150 μs,the material removal rate is increased by 83.8% and the relative tool wear rate,hole taper and surface roughness are decreased by 33.7%,22.3% and 16.4% separately.