The invention relates to the field of chemical synthesis of sex pheromone of insects, in particular to a method for preparing sex pheromone of carpocapsa pomonella, which comprises the following steps of: performing a Wittig reaction of 8-hydroxy octyl triphenylphosphine bromide and 2E-crotonaldehyde in a certain amount of mixed solvent of varsol and an ether solvent under the action of butyl lithium; and after the reaction is finished, inactivating by using a potassium dihydrogen phosphate solid to obtain a target compound. The method has the advantages of simple operation, good product appearance and high yield, low price and cost due to the use of common solvent as the organic solvent, and easy large-scale industrial production. Therefore, the method for preparing the sex pheromone of the carpocapsa pomonella has a great significance for the prevention and control of the carpocapsa pomonella.