The invention discloses a preparation method of an intermediate suberic anhydride of vorinostat. The preparation method comprises the following steps of A, adding certain amounts of suberic acid and acetic anhydride into a multi-mouth flask respectively, and placing the flask into a heat collection type constant temperature heating magnetic agitator; B, controlling certain heating temperature and reaction time, wherein the heat collection type constant temperature heating magnetic agitator is provided with reduced pressure distillation at the same time; C, carrying out the reduced pressure distillation while a reaction is carried out in a reaction process, shifting out acetic acid, which is one of products, regulating pressure, continuously carrying out the reaction, carrying out in-situ pressure reduction at a later period of the reaction, and distilling and removing the unreacted acetic anhydride; D, after the reaction is terminated, directly adding a devitrifying solvent into a reaction bulb, carrying out cooling and crystallization, and carrying out suction filtration, washing and vacuum drying, so as to obtain white solid suberic anhydride. The method is easy and feasible, and is simple and convenient to operate; the progress of a positive reaction is greatly accelerated; the unreacted acetic anhydride is duly removed through the reduced pressure distillation in the reaction process; the process of the post treatment is simplified; moreover, the devitrifying solvent is directly added after the reaction is terminated; a high-purity target product suberic anhydride is obtained.