The ordersCellvibrionales,Oceanospirillales, andPseudomonadales, as three major orders of the largest bacterial class,Gammaproteobacteria, play important roles in various ecosystems as the keystone taxa of microbiomes, but their evolutionary relationship is currently polyphyletic and chaotic. Here, we constructed a bac120 tree and core-genome tree and calculated the amino acid identity (AAI) value to explore their intrinsic evolutionary history. In this study, we proposed two novel orders and three novel families. This evolution study vastly reconstructed the taxonomic framework of classGammaproteobacteriaand could provide a more distinct perspective on global distribution and evolutionary patterns of these environmental microorganisms.