Preparation: Add isononanoic acid (300 g, 1 eq.) to a 500 mL reaction bottle, and introduce phosgene (1-5 eq.) at a certain temperature and a certain speed, and monitor the reaction process by gas chromatography. After the reaction is completed, dry nitrogen is introduced into the reaction mixture to replace the unreacted phosgene, by-product carbon dioxide and hydrogen chloride, and then 3,5,5-trimethylhexanoyl chloride is obtained by vacuum distillation as a colorless liquid.