The invention belongs to the technical field of coal mine safe production, and discloses a gas adsorbent and a preparation method thereof. The preparation method comprises the following steps that a microporous metal substrate soaked in a nano catalyst is heated to be 300 DEG C at the speed of 3 DEG C/min under the protection of inert gas, and then subjected to heat preservation for 2 hours, and acarbon-containing compound is guided into the substrate; the substrate is heated to be 600 DEG C at the speed of 10 DEG C/min, and heat preservation is conducted for 1 hour; the substrate is heated to be 1000 DEG C at the speed of 25 DEG C/min, and cooled to be the room temperature at the speed of 10 DEG C/min, and porous graphene is obtained; the porous graphene is evenly mixed with a carbon nano tube, mechanical blending is conducted, and the multi-dimensional pore structure graphene compound is obtained; the compound is dipped into a surface active agent and placed in the environment of decompression and at the temperature of 35 DEG C or below for 2 hours, and the multi-dimensional pore structure graphene compound adsorbent is obtained. The gas adsorbent is high in adsorption amount and high in adsorption rate, and the preparation method is simple, and easy to industrialize.