The operation principle of main unit of GTM Medium Speed Trapezium mill is that main unit runs with the central shaft that is driven by a gear box. The top of the shaft is connected with a quincunx stand on which a grinding roller is installed to form a swing support. The grinding roller not only rotates around the central axle and grinding ring but also rotates around its own axle due to the friction. There is a pallet knife system at bottem of quincunx stand. The pallet knife system is under the grinding roller. With co-rotation of pallet knife and grinding roller, pallet knife will lift the materials into the space between roller and ring to to form a material layer. The materials will be grinded due to the centrifugal force of roller and thus finally achieve the aim of making powder.