The effect of Trichogramma dendrolimi carrying Bacillus thuringiensis on controlling Ostrinia furnacalis was evaluated in cornfield. The results showed that the parasitism capacity of the Trichogramma carrying bacteria was not different from that of Trichogramma without carrying the microbial. But the controlling efficiency was 13.95% higher than the later on average, 15.21% the highest. Search of host plant and parasitism activities of Trichogramma dendrolimi in the field was helpful to the transmission of pathogenic bacterium, therefore, increased the mortality of Ostrinia furnacalis larvae remained in the fields.