The 2.1 kb fragment of enhancin gene from Helicoverpa armigera granulosis virus was inserted into vector pQE-30 and expressed successfully in E. coli M15(pREP4). The synergy of expression product(P78) on AcMNPV against the larvae of Plutella xylostella was also studied. The results indicated that the percentage of correct mortality of the larvae increased 27.88%-32.92% in 10 post-infection days.