Polycyclic aromatic hydrocarbons (PAHs), which consist of two or more fused aromatic rings, are ubiquitous pollutants in the environment, and are of concern because of their toxic and carcinogenic potential. In nature, the aerobic bacterial bio-treatment of contamination with PAHs is of the major route. It is obvious that the degraders are more useful for the bioremediation of contaminated environments and may be potentially used in a wide of application. Therefore, many researchers have been focusing on the biodegradations of PAHs by various aerobic bacteria. In the last two decades, the mechanism of degradation in bacteria capable of aero-biotic utilizing PAHs has been well investigated in genetic studies such as diversities of genes of PAHs metabolism, the genes which participate directly in PAHs metabolism and the genetics mechanism of bacterial population and so on. In brief, most of PAH-catabolic genes are classed into two groups according to their identity. One group is called “the nah-like genes”, the other group, i.e. “the nah-unlike genes” is different from the nah-like genes. The different molecular genetics mechanisms of bacterial population adapted to PAH compound will be dealt with in three groups: (i) point mutations, (ii) gene transfer, and (iii) DNA rearrangements and absentation. In this review, some genetic knowledge about aerobic bacteria with the mechanism for the degradation of PAHs is summarized.