The biodcgradation of benzene and toluene was studied by aquifer material microcosm experiment in laboratory under enhanced denitrifying conditions. Based on analyses and contrast of the experiment results, the following important conclusions were obtained. Microorganisms can utilize nitrate as the electron acceptor to degrade benzene and toluene under enhanced denitrifying conditions. The denitrifiers come from the aquifer material. The macro-nutrient that microorganisms need is provided by benzene, toluene and nitrate, and the trace elements come from the aquifer material. Environmental conditions have great effects on the biodegradation of benzene and toluene, and the pH values strongly inhibit the biodegradation when they are too high or too low.