The invention relates to a preparation method of resin-based spherical activated carbon with a controllable pore structure. The preparation method comprises the following steps: adding a phenol and an aldehyde into water according to the molar ratio of 1: (2-6), adding a catalyst accounting for 0.7-1% of the molar amount of the phenol into a solution, heating and increasing the temperature to 85-90 DEG C under stirring conditions, then adding a dispersant accounting for 10%-30% of the molar amount of the phenol, continuously stirring for 20-60min, then adding a curing agent accounting for 1%-3% of the molar amount of the phenol and a pore-forming agent accounting for 0-5% of the molar amount of the phenol, continuously stirring for 2-5h, cooling to room temperature, and filtering to obtain resin spheres; and carbonizing the prepared resin spheres under the protection of nitrogen, further activating, and reducing the temperature to room temperature to obtain the phenolic resin-based spherical activated carbon. The preparation method provided by the invention has the advantages of controllable aperture, mild operation conditions and low cost.