The invention discloses a synthesis method of Megastigmatrienone. The method is characterized by comprising the steps: performing oxidation on alpha-ionone by using tert-butyl hydroperoxide under thecatalysis action of Vanadiumoxy Acetylacetonate so as to generate 3-oxo-alpha-ionone, performing hydroboration on 3-oxo-alpha-ionone in an ethanol solution so as to obtain 3-oxo-alpha-ionol, adding solid p-toluenesulfonic acid directly, and performing reflux dehydration so as to obtain Megastigmatrienone. The method has a simple process and simple conditions, and is more beneficial to industrialized production.