The invention relates to an insecticidal gene and applications thereof. Nucleotide sequences of the insecticidal gene comprises: (a) nucleotide sequences represented by SEQ ID No.3; or (b) nucleotide sequences that contains the same code of the (a) nucleotide sequences, and is not represented by SEQ ID No.22; or (c) nucleotide sequences which is hybridized with nucleotide sequences limited by the (a) nucleotide sequences or the (b) nucleotide sequences under strict conditions, and is capable of coding a protein with insecticidal activity. The insecticidal gene provided by the invention is particularly suitable for being expressed in monocotyledon, so that expression quantity, stability and toxicity of Vip3Aa-01 insecticidal protein are remarkably improved. In addition, the insecticidal gene is capable of controlling sesamia inferens walker by generation of Vip3A protein in plants, realizing protection on the whole growth period and the whole plant, and preventing attack of sesamia inferens walker, wherein Vip3A protein is capable of killing sesamia inferens walker. No pollution or residual is caused; effect is stable and excellent; utilization is simple and convenient; and cost is low.