To explore the genetic diversity of Dosidicus gigas in the Southeastern Pacific Ocean and its relationship with environmental factors, this study analyzed the genetic diversity of three phenotypic groups （large, medium, and small） and the impact of environmental factors using mitochondrial COⅠ gene data, redundancy analysis （RDA）, and Mantel tests. The results showed that the overall haplotype diversity （H_d） of D. gigas populations was 0.455, while nucleotide diversity （π） was 0.001 1, indicating high H_d and low π. The genetic differentiation coefficient （F_st） between populations was less than 0.05, gene flow （N_m） was greater than 1, and within-group variation accounted for 99.14% of the total. Genetic data suggested that the populations underwent a historical expansion event approximately 46 700 years ago. RDA and Mantel test results indicated a weak correlation between geographical distance and mean genetic distance, while latitude （lat）, sea surface temperature （SST）, sea surface salinity （SSS）, and pH were significant environmental factors influencing the genetic diversity of D. gigas populations （P<0.05）. Furthermore, the distribution of different phenotypic groups was influenced by distinct environmental factors. The study concluded that there was no significant genetic differentiation among the three phenotypic groups of D. gigas, but environmental factors had a significant impact on their genetic diversity. This research provides valuable reference data for the conservation and management of D. gigas populations.