The invention relates to a synthetic method of trimethylolpropane tricaprylate, which belongs to the technical field of esters compound synthesizing in organic chemistry. Taking trimethylolpropane and isocaprylic acid as material, an esterification reaction is preformed in nitrogen gas under the action of metallic oxide catalyst, the trimethylolpropane tricaprylate is obtained after depickle and filtration; the mass ratio of the trimethylolpropane and the isocaprylic acid is 1:3.15-3.95; the metallic oxide catalyst is stannous oxide or ferric oxide or magnesia, and the like, and the adding amount of the catalyst accounts for 0.03 to 0.10 percent by weight of the total weight of the trimethylolpropane and the isocaprylic acid. The invention reasonably selects metal oxide as the catalyst, and the metal oxide does not erode equipment, can be removed by filtration after the reaction is finished and can be recovered for recycle use; and the invention has advanced and reasonable process andless equipment investment through reasonable regulation of the adding amount of the trimethylolpropane and the isocaprylic acid and the proportion of the metal oxide catalyst and the optimal selection of reaction temperature and reaction time.