The invention provides a waterproof anticorrosion agent for cement mortar and concrete and preparation thereof, and belongs to the field of building material waterproof anticorrosion agents. The waterproof anticorrosion agent comprises stearic acid, oleic acid, polyvinyl alcohol, a surfactant, sodium hydroxide and an anticorrosion corrosion-inhibiting agent with the mass ratio of 30-40:20-30:3-5:30-40:2-3:1-5. The preparation method of the agent comprises: preparing a sodium hydroxide solution; mixing stearic acid, oleic acid and polyvinyl alcohol, heating to 100-130 DEG C, so as to obtain a mixed solution; and adding the sodium hydroxide solution into the mixed solution, performing warm-keeping reaction, then adding the surfactant and the anticorrosion corrosion-inhibiting agent, continuing the reaction, and then stopping heating and cooling. The waterproof anticorrosion agent has the advantages of excellent waterproof and anticorrosion performances, firm structure, long service life, simple and convenient construction, short production period, low cost and the like.