In the paper, the Molecular Dynamics (MD) simulation model and the Finite Element (FE) analysis model were combined together to study the mechanism of the Electrolytic In-process Dressing (ELID) grinding. A 3-D MD simulation model for grinding monocrystalline silicon was established to acquire grinding force and its change laws, and an interpolation multinomial of grinding force was established on the basis of MD simulation result. A FE model for abrasives and the passivation film was established to calculate displacement of abrasives in the passivation film. The grinding force and abrasives displacement were iterated between MD simulation model and FE analysis model to obtain the displacement variation of the abrasives in the passivation film. The simulation result shows that, the uniform height of the abrasives in the contour of the grinding wheel is improved owing to the existence of passivation film in ELID grinding, it is related to the thickness of the passivation film, and processing quality in ELID grinding could be enhanced through controlling of thickness of the passivation film.