Using the tiny-grinding wheel based on the synergistic effect of the electro-magneto- rheological (EMR) fluid, a novel method is presented to machine the three-dimensional (3D) microstructure of hard-brittle materials. Machining experiments of micro-groove were conducted to reveal the machining performances of the tiny-grinding wheel. Experimental results confirm the effectiveness and feasibility of the micro machining technique with the EMR effect-based tiny-grinding wheel. The shape of machined micro groove is found to be an inverted trapezoid, and the material removal mode of normal glass with the micro machining method is the plastic-removal mode. With the increase of the rotation speed of the tool, the material removal rate, width and depth of micro grooves increased first and decreased afterwards. The maximum removal rate, width and depth of micro groove occur at different speeds of the tool.