The invention provides a preparing method for 3,5-bis(tertiary butyl)-4-hydroxybenzoic acid hexadecane alkyl ester. The preparing method comprises the steps that 3,5-bis(tertiary butyl)-4-hydroxybenzoic acid, cetyl alcohol and a catalyst are added into a reaction vessel, flow of inert gas is introduced, a heat-preserving reaction is carried out at the temperature of 80 DEG C-160 DEG C, TLC tracks and monitors the reaction till the reaction endpoint, and reaction liquid is subjected to after-treatment to obtain 3,5-bis(tertiary butyl)-4-hydroxybenzoic acid hexadecane alkyl ester. By means of the preparing method, it is unnecessary to adopt other solvent, production cost is saved, and waste gas exhaustion of organic solvent is avoided in the synthesis process; the inert gas serves as a water-carrying agent and a protective agent, operation and control are simple, production safety is good, the color of products is improved, and the method has remarkable economic benefits and has remarkable environmental protection significance.