Abstract: Based on the electro-magneto-rheological (EMR) effect, the Fe3O4-based EMR fluid dispersed with micron-sized finishing abrasives is used as a polishing fluid to form a dynamical tiny-grinding wheel under electro-magnetically coupled field. Using this EMR effect-based tiny-grinding wheel, polishing experiments were conducted to investigate the material removal amount of normal glass under the different electro-magnetically coupled fields, and revealed the machining performance of the tiny-grinding wheel. A mechanical model of dispersed particles in the EMR fluid was presented based on the theoretical analysis of materialogy and electromagnetism, and the synergistic effect of the coupled field in polishing with the tiny-grinding wheel was investigated in detail. Experimental results indicated that the material removal amount of the EMR effect-based tiny-grinding wheel was 1.74 times that of the ER effect-based tiny-grinding wheel and 5.71 times that of the MR effect-based tiny-grinding wheel due to the marked synergistic effect of the coupled field. The combined effect of the electric field force, the magnetic field force and the spin couple generated by the Lorentz force determined the stability of the chains of EMR particles and the machining performance of the EMR effect-based tiny-grinding wheel, and a good synergistic effect of EMR fluid can be obtained under appropriate electro-magnetically coupled field.