Abstract: According to the machining requirements of high efficiency and low damage of silicon nitride ceramic rotary surface parts,an electrolytic in-process dressing(ELID)grinding experiment device is designed,which is suitable for rotary surface machining.Pre-dressing experiment is carried out on CNC coordinate grinder.Based on the parallel electrode electrolytic cell model,a model of the relationship between pre-dressing time and oxide film thickness is established,and the influence of the duty cycle and the pole clearance on the film formation is analyzed as well.Resultsshow that duty cycle influences pre-conditioning time most,followed by electrolyte flow rate,grinding wheel speed and pulse frequency.In conclusion,the optimal process parameters are duty cycle 0.75,pulse frequency 50 kHz,wheel speed 9 000r/min,and electrolyte flow rate 1.0L/min through Taguchi method.