The invention discloses a nano graphite fluid for reinforcing coal bed gas purification. The nano graphite fluid adopts nano graphite particles, a base solution, a dispersant and a thermodynamic additive as the raw materials. The preparation method of the nano graphite fluid includes: subjecting the nano graphite particles, the base solution, the dispersant and the thermodynamic additive to mechanical stirring and performing dispersion by an ultrasonic dispersion instrument to obtain nano graphite fluid, i.e. an adsorbent. The preparation method of the nano graphite particles include: subjecting graphite to ball-milling in liquid carbon dioxide to a particle size of 0.1-0.2mm, then performing pressurization on the milled graphite and liquid carbon dioxide at room temperature, conducting placement under the pressure for 30-45min, then raising the temperature to 150-200DEG C, and releasing the pressure to normal pressure within 3min, thus obtaining the nano graphite particles with a particle size of 20-80nm. The CH4 recovery method provided by the invention is simple, the cost is low, and the methane recovery rate of low concentration coal bed gas is greatly increased.