The clinically isolated Klebsiella pneumoniae (K. pneumoniae), a rod-shaped Gram-negative bacteria with capsular, is an important opportunistic pathogen in clinic. There are genetic differences among clinical isolates of K. pneumoniae. Strains can be divided into K. pneumoniae (KpⅠ), K. quasipneumoniae (KpⅡ) and K. variicola (KpⅢ) three groups according to the phylogenetic tree. There are significant differences in ecological distribution, genotype, drug resistance, virulence characteristics, and pathogenicity among this three groups, which brings new challenges to the precise treatment of infectious diseases. In this article, the latest studies of identification, epidemic characteristics and pathogenic characteristics of K. pneumoniae, K. quasipneumoniae and K. variicola are reviewed.