The invention relates to application of a cry2Ah-vp gene in armyworm resisting. The applicant inserts a proline behind No. 354 bit valine of cry2Ah and a cry2Ah1-vp mutant shown as the SEQ ID No. 1 isobtained accordingly. The cry2Ah-vp gene is obtained after codon optimization, the cry2Ah-vp gene is transplanted into maize with an agrobacterium-mediated method, and T0 generation transgenic maizeis obtained. The experimental result shows the cry2Ah-vp gene can be normally transcribed into different tissues of the maize, the expression quantity of the cry2Ah-vp protein in all parts of the maize is the maximum in the six-leaf stage, the leaf expression quantity is 2.20 mu g/g (fresh weight), and all parts have higher expression in the tasseling stage and the filling stage. The insect resisting experiment result shows that the transgenic maize has good insecticidal activity to the armyworms, and the armyworms are all dead after inoculated to the maize three days; the cry2Ah-vp gene has aremarkable growth inhibition effect to the ostrinia nubilalis larvae.