The invention relates to a gas sealing mechanical structure, in particular to a dynamic sealing structure for multi-freedom-degree slide rods. By means of the dynamic sealing structure, high-temperature harmful gas is effectively stopped from being leaked in multi-freedom-degree motion. According to the dynamic sealing structure, an inner seal cover is fixedly connected to a shell, and an outer seal cover is linked to the inner seal cover; slide blocks slide in a cavity formed by the inner seal cover and the outer seal cover; by means of guide rods, it is guaranteed that the slide blocks slide in the Y direction all the time; by means of a tightly-pressing device, tightly-pressing force of each spring is changed through a corresponding adjusting screw, and by means of the tightly-pressing force of the springs, it is guaranteed that the slide blocks are tightly pressed through universal ball bearings; each slide rod is sleeved with an axial seal joint, so that axial sliding and deflection are achieved; and each graphite packing is tightly pressed into a clamping groove in the inner side of a corresponding joint bearing through a pressing ring, and thus each graphite packing is closely attached to the corresponding joint bearing and the corresponding slide rod. By means of the sealing structure, sealing of the slide rods in multi-freedom-degree motion is achieved, and environmental harm caused by leakage of the high-temperature harmful gas is effectively prevented; and in addition, the sealing structure is simple in structure, reasonable in design, easy to mount and maintain and long in service life.