The present invention discloses a novel underground spray coating material and a preparation method thereof, and belongs to the technical field of mine protection engineering. According to the present invention, a polymer cement base slurry comprises an additive, cement and water, wherein a ratio of the additive and the cement to the water is 1:1, and the additive comprises the following components, by weight, 50-65% of 425 cement, 15-23% of an acrylic acid powder material, 5-8% of gypsum powder, 3-6% of calcium carbonate, 2-4% of a high strength water reducing agent, 4-7% of an accelerated agent, and 1-2% of antifoaming agent. The preparation spray coating method comprises material preparing, stirring, spray coating and the like. According to the present invention, in the case of the same viscosity of the cement slurry, a spraying performance of the polymer cement base slurry is significantly improved; a bonding performance of the material and the surrounding rock is substantially improved; and compared to the ordinary cement slurry, a tensile bond strength of the cement base slurry is increased by about 100-300%, and a 14 d shear bond strength can be increased by 100-140%.