Antibiotic resistance genes (ARGs) in aquatic environments, which seriously endanger human health and ecological safety, have become a worldwide concern due to their easy diffusion and proliferation. Wastewater treatment plants (WWTPs), which receive resistant bacteria and ARGs from a wide variety of sources (i.e., livestock farms, hospitals, antibiotic manufactures, and households), are regarded as important emission sources of aquatic ARGs. This review presents a quantitative profile of the majority sources of ARGs in the influent of WWTPs and discusses the potential factors that affect the concentration distribution of ARGs. Specifically, a noteworthy existence of ARGs, which ranged from 1E+05 to 1E+11 copies/mL, was detected in livestock breeding wastewater, and household wastewater (caused by the unlimited utilization of antibiotics) was determined to be the predominant contributor of ARGs in WWTPs. We summarized the selective pressure on ARGs and determined the positive correlation of the concentration of ARGs and the existence of many containments, including antibiotics, heavy metals (Zn and Cu were frequently reported), quaternary ammonium compounds, etc. In the last section, physical, chemical, and biological treatments for the removal of ARGs and their effluent in WWTPs are discussed and prospective future studies are summarized.