The invention discloses a preparation method of an oceanographic engineering reinforced concrete structure surface protective agent. The preparation method of the oceanographic engineering reinforcedconcrete structure surface protective agent adopts a sol-gel acid-base two-step process; a composite material of nanometer silicon dioxide particles and a chain type small molecular silicon polymer issynthesized; the chain type small molecular silicon polymer is used as a main film-forming substance; the nanometer silicon dioxide particles are adopted for interface modification, the oceanographicengineering reinforced concrete structure surface protective agent is directly used for surfaces of newly-built concrete, permeation into the deep parts of concrete and reaction on alkaline surfacesto generate inorganic inert hydrophobic films are realized, water vapor discharge channel are reserved, corrosion of corrosive mediums in the marine environment is avoided, and the characteristics ofrapid curing, remarkable corrosion prevention effect and the like are achieved.