The invention relates to an improved preparation method of a paint applied to the internal surface of an oil tank. The paint is composed of the following components in percentage by weight: 10-25 wt% of curing agent, 10-25 wt% of methyl cellulose, 15-65 wt% of silica sol, 20-45 wt% of corrosion-resistant water-based pigment and filler paste, 20-80 wt% of ammonium polyphosphate, 20-55 wt% of microparticle silicic acid, 20-40 wt% of drying agent, 50-80 wt% of solvent, 20-60 wt% of preservative, 10-30 wt% of defoamer, 2-10 wt% of water-based assistant, 30-60 wt% of deionized water, 4-10 wt% of polyoxyethylene enzyme, 10-25 wt% of barium sulfate and 1-10 wt% of hydrogenated castor oil. The paint has the advantages of favorable corrosion resistance, high temperature resistance, favorable oxidation resistance, favorable scrub resistance and the like, has an antiseptic effect inside the oil tank, and can not easily generate chemical reaction with the liquid (turpentine, methanol and the like) in the oil tank; the construction technique is implemented by pouring the paint into the oil tank, uniformly shaking and pouring out, and thus, is simple; the paint can be closely combined with the base material immediately, and can not easily shed; and the method has the advantages of simple preparation process and low cost, and can easily implement industrialized mass production.