The guiding mechanism is composed of a drag plate, a pair of pre-tightened roller linear guide rail and an additional pressure unit. The pressure unit includes an oil cylinder, a wedge-shaped block and a guide rail. When the gear box fast forward into the working time, the cylinder pushes the block to fix the flat guide rail tightly, so as to effectively transfer the cutting force acting on the saw blade to the frame, reduce the tipping moment generated on the main rail, and improve the working life of the guide mechanism; During non-cutting working hours, the cylinder rod is withdrawn to reduce the load on the feed mechanism. The additional slide rail is at the same level as the lowest position, and can accommodate the largest diameter of the saw blade, on this basis, better transfer the cutting force to the frame to protect the guide rail