The phylogenetic diversity of marine bacteria belonged to the Bacillus cereus group has not been well investigated. Here, we present the genetic diversity and population structure of 71 bacteria from diverse marine environments, using a multilocus sequence typing (MLST) approach and the analyses of digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) based on some representative genomic sequences. The MLST analysis demonstrated that these isolates were highly diverse and a wide distribution in marine environments and some of them showed niche specificity to some extent. They were assigned to 27 sequence types (STs) with 23 novel STs. Phylogenetic analysis of 82 bacteria containing 11 type strains based on MLST discriminated them as 20 clusters including 10 new ones. Both the dDDH and ANI results supported the proposition that each of 20 clusters represented one independent species, including 10 putative novel species. Values of 98.3% of MLST similarity and 96.2% of ANI were proposed as the standard for the species definition of this group. In summary, the first insight into the phylogenetic diversity of the group bacteria from marine environments will contribute to better understanding of their ecological role and evolution in contrast with terrestrial environments.