The invention relates to a method for preparing an antioxygen 1790 intermediate through a solvent-free method. The intermediate is specifically 2,4-dimethy-6-tertiary butyl-3-chloromethyl phenol. Thepreparing method of the antioxygen 1790 intermediate comprises the steps of reacting 2-4-dimethyl-6-tertiary butyl phenol, paraformaldehyde and concentrated hydrochloric acid under the effect of a catalyst at the room temperature, and in the reaction process, continuously introducing gas HCL, wherein the catalyst is a mixture of an ionic surfactant and a nonionic surfactant. The conversion rate ofraw materials is high, and the conversion rate of 2,4-dimethy-6-tertiary butyl-3-chloromethyl phenol can reach 99% or above; a solvent-free technology is adopted, and compared with an existing technology of adopting haloalkane as a solvent, the method has obvious environmental protection performance and low toxicity; the ionic surfactant and the nonionic surfactant are compounded for a catalysisreaction, the dosage of the catalysts is sharply lowered, and the cost is saved; the reaction can be completed simply under the room temperature, and the condition is mild.