Ultrasonic vibration electrical discharge machining (EDM) is a new machining method for machining micro-holes with high efficiency,which can improve the machining efficiency and accuracy.Micro-hole machining by longitudinal-torsional ultrasonic vibration EDM was studied.A mathematical model was established to describe the flow characteristics of the working fluid in the clearance around electrode wire,and Fluent was used to verify the mathematical model.At the same time,the debris was added to explore the movement of the working fluid in the clearance and debris removal.The results show that during EDM,the longitudinal-torsional ultrasonic vibration has obvious torsional motion in the fluid domain.Due to the increase of the torsional motion,it is beneficial for the debris to enter the side gap from the bottom gap,and to be discharged from the holes with the flow of the working fluid.The debris accumulation at the bottom is effectively prevented,which can improve the accuracy of the EDM hole.