In order to study the phylogenetic relationship of Euphausiacea, 50 Euphausiacea species were selected and used for the construction of a phylogenetic tree. The mitochondrial COI gene was amplified using PCR techniques. The results showed that a 519 bp COI gene fragment was obtained and sequenced, with 258 mutation sites, all of which were base substitutions, and no insertion/deletion sites. The contents of A, T, G, and C were 27.58%, 35.47%, 18.88%, and 18.07% respectively. Additionally, the content of A+T (63.05%) was significantly higher than that of G+C (36.95%). The genetic distance within species ranged from 0 to 0.071 and the average value was 0.017. The genetic distance among species ranged from 0.065 to 0.306, and the average value was 0.186, which was about 11 times that of the former. With regards to the minimum interspecific genetic distance of 0.020, the difference between the COI gene sequences could distinguish the Euphausiacea species efficiently. Four phylogenetic trees were constructed:neighbor-joining tree (NJ), maximum likelihood tree (ML), maximum parsimony tree (MP), and UPGMA tree. Their topological structures were basically the same, i.e. they can be divided into three branches. Pseudeuphausia was on the bottom of the phylogenetic tree, which was one of the earlier species of Euphausiacea. The Euphausia, which contained the most species, finally was branched out, indicating that it was a relatively newer genus of Euphausiacea. The phylogenetic relationships among 11 Euphausiacea genera have been comprehensively discussed in this paper. The results showed that the phylogenetic tree constructed based on the mitochondrial COI gene could be used to study the phylogenetic relationships between the Euphausiacea species and was of notable theoretical and practical value.