The invention provides a composite for increasing the mating ratio and mating time of diamondback moths. The composite is prepared by blending, by mass, 1-10 parts of octanal, 5-20 parts of hexyl alcohol, 5-20 parts of geraniol, 5-20 parts of benzyl alcohol and 5-50 parts of cis-3-hexene acetate. The composite is a volatile substance screened out from multiple host plants of the diamondback moths, and has the advantages of being significantly effective, harmless to moth bodies and the like. In the presence of the composite, the mating ratio of the male diamondback moths and the female diamondback moths can be increased, the mating time of the diamondback moths can be prolonged, the egg laying quantity of the female diamondback moths is easily improved, especially when artificial feed is adopted to feed the diamondback moths, the moderate release of the composite significantly improves the reproduction efficiency of offspring, and an excellent time guarantee is provided for tests for researching diamondback-moth mating selection behavior diversity.