The present invention provides a trimethyl orthoacetate synthesis method, wherein acetonitrile and methanol are adopted as starting raw materials. The method comprises: 1) when acetonitrile, methanol and a non-polar solvent are subjected to mixing cooling in a reaction kettle to achieve a temperature of -20 to -5 DEG C, adding a small amount of a Gemini surfactant to the system, then introducing dried hydrogen chloride gas to make a molar ratio of acetonitrile to methanol to hydrogen chloride to the surfactant be 1:1-2:1.05-1.5:0.001-0.005 and make a mass ratio of acetonitrile to the non-polar solvent be 1:2-5, and carrying out a complete stirring reaction after introducing the hydrogen chloride gas so as to generate an ethylenediamine methyl ether hydrochloride; and 2) adding methanol having the amount 2-4 times the molar amount of the starting acetonitrile is added to the ethylenediamine methyl ether hydrochloride generated in the step 1), adjusting the pH value of the reaction system to 5-6.5, carrying out an alcoholysis reaction at a temperature of 25-40 DEG C, filtering the alcoholysis product, and refining to obtain the trimethyl orthoacetate. With the method of the present invention, the water content of the original ester synthesis system can be completely reduced so as to significantly improve the trimethyl orthoacetate yield.