The invention discloses a release agent for lead storage battery grid casting and a preparing method thereof. The release agent for lead storage battery grid casting comprises the following raw materials of, by mass, 100 parts of water, 4-6 parts of cork powder, 1.5-2.5 parts of volcanic ash, 1.5-2.5 parts of sodium silicate and 0.15-0.20 parts of phenolic resin. According to the release agent for lead storage battery grid casting, the volcanic ash of being high-temperature-resistant, high in viscosity, not easy to carbonize and small in particles is added, the fact that the release agent falls off too fast is reduced, the durability of the release agent is increased, the time interval of mould jetting during grid casting is extended, the work efficiency is improved, and the stability of plate grid gram weight is improved; and the water-soluble phenolic resin is added, the release agent has the advantages of heat resistance, flame resistance and water resistance and insulativity, the acid resistance is good, the alkali resistance is poor, the mechanical and electrical performances are good, demoulding is easy, the transfer rate is low, during synthesis, different components are added, the modified phenolic resin of different functions can be obtained, and the release agent has a variety of excellent characteristics such as alkali resistance, abrasion resistance, oil resistance and corrosion resistance.