Abstract: The thesis adopt the inoculation method, studied the maize yield loss and component influence of different grade of diseases and the amount of worm, and studied the mixed damage of maize Ostrinia furnacalis (A), Curvularia lunata (B), Exserohilum turcicum(C), Sphacelotheca reiliana(D) and economic threshold. The result showed that the main damage influence of diseases and worm was thick of ear, grains of row and the weight of one hundred grains, the grade of disease and the amount of worm had significant positive correlation to yield loss; the relationship of diseases and worm was complex, the yield loss of mixed damage was occupied 41.48% of the total damage of the single, the sequence was A＜C＜B＜D＜ABCD＜(A+B+C+D), the simulated models of mixed damage and economic threshold were developed.