To elucidate the mechanism of pyrethroid resistance in Helicoverpa armigera, the study explored three possibilities based on deltamethrin as a model pyrethroid; 1) the existence of mutations in the target site of deltamethrin, 2) the existence of variation at the genomic level between insecticide-susceptible and resistant strains, 3) differences in gene expression patterns between the strains. Based on these hypotheses, three levels of resistant strains and a susceptible strain as well as nine Korean field populations were used. As results, 1) any point mutations were not detected in sodium channel gene. 2) based on newly set Korean reference genome (GCA_026262555.1), approximately 3,369,837 and 1,032,689 variants (SNPs and Indels) were revealed from genome and ORFs, respectively. However, any specific variants were not found to be highly correlated with the level of insecticide resistance. 3) based on DEG analysis, some of detoxification enzyme genes were differently expressed particularly cytochrome P450 genes. Therefore, H. armigera possibly acquires deltamethrin resistance through a combination of actions, including over-expression of various detoxification enzymes such as CYP3 subfamilies and cuticular proteins.