The invention relates to a high pressure maintaining cutting technology, and aims at providing a pressure maintaining cutting device for a natural gas hydrate sampling pipe. The pressure maintaining cutting device for the natural gas hydrate sampling pipe comprises a hollow tubular outer cylinder used for pressure maintaining, a tool feeding and retracting mechanism, a circumferential rotation mechanism and a clamping mechanism; a tool feeding and retracting internal component, a circumferential rotation internal component and a clamping internal component are arranged in the outer cylinder insequence through a bearing and a matched bearing base; and the circumferential rotation speed and radial feeding speed of a tool bit and the clamping speed of a clamping jaw are determined by controlling the rotation speed of a motor. The pressure maintaining cutting device for the natural gas hydrate sampling pipe has the advantages that pressure is balanced, the structure is simple and basically symmetric, and the installation is convenient and simple; cutting is uniform, the disturbance of a sample is reduced during cutting, a sample cutting device does not generate secondary pollution tothe sample, and cutting is carried under pressure maintaining and temperature control conditions; and the cutting depth, the tool feeding and retracting speed of cutting and cutting speed can be controlled accurately.