Based on the principle of confined compression tests, the half mold consolidation apparatus was designed for soil’s microobservation under axial and confined compression stress. Firstly, the macro deformation field of medium sands in half mode test was analyzed and microscopic feature zones were eventually selected: the axisymmetric displacement field was similar to a parabola, the largest change of displacement always occured at the bottom's center of the upper porous stone. By using the micro image processing software——MiFas, micro mechanics characteristics of the tests was further studied, including the whole acreage of granules,the changes of long and short axes, eccentricity, the angle between the long axes and horizontal direction and the void area's ratio. The importance of micro mechanics study lies in its emphasis on the distribution of the deformation field and related micro structural changes. The design of half mold micro observation apparatus was also a creative work for macro deformation and micro structure analysis which could provide a new concept for the development of traditional soil mechanical tests.