Abstract: 【Objective】 The Δ9 desaturase gene in Euzophera pyriella plays an important role in the accumulation of unsaturated fatty acids, so this project aims to clarify the characteristics of the gene and its expression in different insect states. 【Method】 This study aimed to identify, analyze, and predict the nucleotide and amino acid sequences of Δ9 desaturase in Euzophera pyriella(EpFAD9 ) using bioinformatics software, and to deduce the structure and function of the protein. The mRNA expression of the EpFAD9 gene in different stages of E. pyriella was also determined by RT-PCR. 【Result】 The open reading frame of EpFAD9 gene consisted of 1,056 bp and 352 amino acids. The start codon ATG was located at the 1,280 base of the obtained sequence, and the stop codon TAA was located at the 2,338 base of the sequence. It was speculated that the protein had no signal peptide but had four transmembrane domains, which behaved as a hydrophilic protein and played a biological role in the endoplasmic reticulum. The relative expression level of EpFAD9 gene was rich in larval stage, which was 17.75 times and 29.58 times higher than those in adult and sputum stages, respectively. 【Conclusion】 The expression of EpFAD9 gene is different in different Euzophera pyriella states, and the expression level in larva was the highest, while that in adult and pupa was low, the pupa stage is the lowest, this shows that the resistance of pupa and adults to low temperature is lower than that of larvae.