The invention provides a holotrichia parallela sex pheromone synergist and a preparation method and belongs to the technical field of comprehensive prevention and control of holotrichia parallela. The holotrichia parallela sex pheromone synergist is characterized by being prepared from holotrichia parallela sex pheromone, a synergist and an organic solvent. The holotrichia parallela sex pheromone is prepared from L-isoleucine methyl ester, (R)-(-)-linalool and 1-aminocyclohexanecarboxylic acid, the synergist is prepared from cis-9, trans-11-tetradecadien acetate, cis-5, trans-7-dodecadien acetate, honey and mustard oil, and the organic solvent is prepared from dichloroethane, cyclohexane and fatty acid methyl ester. The synergist has the advantages of being sensitive, specific, high in efficiency, long in lasting period, biodegradable, good in biological compatibility, free of environmental pollution, low in cost and the like, can be used for population monitoring of the holotrichia parallela, prevention and control of trapping and killing of a large number of holotrichia parallela and accurate prediction of the density of a next generation of insect populations and has very good economic benefits and ecological benefits.