According to the requirements of high quality machining of composite materials and the advantages of various machining technologies,the two-dimensional ultrasonic vibration composited electrochemical/electrical discharge machining (2UECM/EDM) is proposed in this paper, and surface formation mechanism is deeply studied. Benefiting from the widening of the grooves of the machined surface by the single abrasive particle motion and the levelling effect of electrochemical/electrical discharge machining, the change in the surface topography and surface roughness (Ra) of composite materials were analyzed by the grinding area ratio (δ_s).Surface formation mechanism of 2UECM/EDM was experimentally compared.The results show that single-cycle feed distance,voltage and two-dimensional ultrasonic amplitude affect the surface quality. Among them, the trend of Ra change is consistent with the feed distance of abrasive particles in a single cycle.The effect of electrochemical/electrical discharge machining is obvious at higher voltage,which leads to the exposure of reinforced particles and increases Ra.The δ_s increases significantly under axial and tangential vibration, and Ra shows an obvious turning trend near 1.8.Therefore,when greater δ_s amplitude and lower voltage are selected,the dragging and rolling of the reinforced particles during processing can significantly reduce Ra and greatly improve the surface quality of the workpiece.