The invention relates to a device for generating a high-saturation methane hydrate sediment sample and a method for generating the sample. The device comprises a mould, wherein a cavity for installing a piston is arranged in a mould; the bottom of the piston and the cavity form an accommodating region for generating the sediment sample; a thermoelectric coupler is arranged in the cavity of the mould, and the detected temperature information is transmitted to a computer control system by the thermoelectric coupler via a data acquisition system; the outside of the mould is sequentially provided with a holder and a heat exchanger; the mould, the piston, the holder and the heat exchanger form a reaction kettle body; the bottom of the reaction kettle body is provided with a gas storage tank loop, a methane gas aerating loop, a vacuum pumping loop and a pressure detection loop; the methane gas aerating loop is in parallel connection with the gas storage tank loop and the vacuum pumping loop, and then is communicated with the bottom of the cavity of the mould through the pressure detection loop; and exhaust vents of the piston are in parallel connection with a tail gas collecting loop, an gas exhaust pipeline and a tail pressure control pipeline through a connecting pipeline. The device and the method can be widely applied to the field of measuring of basic physical properties of the natural gas hydrate.