The invention belongs to a preparation method of phenolic resin, and provides thermosetting phenolic resin for 3D printing and a preparation method of the thermosetting phenolic resin for 3D printing in order to solve the technical problem that the performance of traditional resole resin cannot completely meet 3D printing requirements. According to the invention, thermal response dynamic crosslinking points are increased, the strength of the resole is improved, the ratio of hydroxymethyl is reduced, and the storage stability is improved. The dimethylglyoxime in the modifier can be dynamically dissociated after being heated, and can quickly form a coordination cross-linking effect with copper ions after being cooled, so that the processing problem caused by viscosity rise is prevented while the strength is improved. The modified A-stage phenolic resin obtained by the preparation method provided by the invention can meet the requirements of 3D printing on low viscosity and rapid hardening of resin.