The invention relates to the field of corrosion protection of ocean engineering materials, and aims to provide a preparation method for an ocean engineering reinforced concrete silane emulsion protective agent. The method comprises the following steps of: previously stirring and dissolving an emulsifier in a reaction kettle by using 40-80 parts by mass of de-ionized water; slowly adding 20-60 parts by mass of silane monomer under high shear force; and then emulsifying at 30-60 DEG C under low-speed stirring for 6-12 hours to obtain uniform stable micro-nano emulsion, namely a product. By using the method, 90 percent of surface water absorption can be reduced, the effect of obstructing erosion of concrete reinforcement by a marine corrosion medium can be achieved, an internal vapor discharge passage is also kept, and internal atmospheric pressure produced to a film layer is reduced. Compared with a pure silane monomer impregnant, the volatilization rate is low, the utilization rate of silane is increased, the infiltration distance is increased, and the full curing time is greatly shortened. Compared with the conventional polysiloxane emulsion, the process is simple, the molecular weight of a filming substance is smaller, the infiltration capacity is stronger, and the filming capacity is higher.