The invention belongs to the technical field of energy conservation and emission reduction, and discloses a method for preparing carbon microspheres from waste phenolic foam as a raw material. The method comprises the following steps: heating 40-60g of waste phenolic foam, 200-400g of water and 0.4-0.6g of acacia gum powder to 90-100 DEG C, performing heat-preservation reaction for 3-5 hours with stirring, cooling, filtering, washing, and drying so as to obtain phenolic resin microspheres; and carbonizing the prepared phenolic resin microspheres, and activating, thereby obtaining target products, namely the carbon microspheres. The carbon microspheres prepared from the waste phenolic foam as the raw material have a good degree of sphericity and a good specific surface area, and have a relatively good adsorption rate on microparticles and harmful gases. The carbon microspheres ensure good spherical shapes without reducing specific surface areas and adsorption capacities of carbon microspheres, an effective utilization mode is provided for the waste phenolic foam, the targets of low carbon, energy conversation and emission reduction are met, and the situations that conventional waste phenolic foam is low in utilization rate and poor in regeneration effect are alleviated.