The invention discloses a preparation method for a circular pressure reinforcing agent for a negative ion semi-chemical corrugated paper, which comprises the following steps: first, evenly mixing methyl metharcrylate, acrylonitrile, negative ion monomer, and oil soluble initiator; then adding the resultant mixture into isopropyl alcohol, acetone or N, N-dimethyl formamide for polymerization, and subsequently removing organic solvent by means of pressure reduction and distillation to obtain water soluble copolymers; next, mixing and pre-emulsifying styrene, methyl methacrylate, acrylonitrile and the water soluble copolymers, finally, initiating polymerization of the mixture by use of ammonium persulphate. The preparation method can be adopted to prepare stable emulsified circular pressure reinforcing agent without using any micromolecular emulsifying agents.