The invention relates to a surface sizing agent for paper making, which has the material formula with a plurality of components and weight percentages as follows: starch 6.5-8%, styrene 4.5-6%, acrylonitrile 4-5%, n-butyl methacrylate 5.5-6.5, methacrylic acid iso-octyl 2-3.5, iso-octyl acrylate 0.4-1%, hydrogen peroxide 0.2-0.5%, formic acid0.5-1%, ferrous sulfate 0.5-4%, n-dodecyl mercaptan 0.5-3%, amylase 0-0.2% and water the rest, wherein at least one is chosen from n-butyl methacrylate, methacrylic acid iso-octyl and iso-octyl acrylate. The appearance of the surface sizing agent is slight yellow emulsion, and the main component is styrene-acrylic copolymer which is easily soluble at normal temperature. The surface sizing agent for paper making has the advantages of greatly increasing paper surface intensity, decreasing hair and powder shedding, and improving the sizing degree, smoothness and printability of paper.