Abstract: Conventional liquid-liquid extraction (LLE) methods usually use water immiscible organic solvents as the extraction solvents and achieve phase separation through repeated shock or multiple extractions. In this paper, a new method for the determination of benzo(a)pyrene and benzo(e)pyrene in groundwater by High Performance Liquid Chromatography (HPLC) with acetonitrile-(NH₄)₂SO₄-water extraction system is described. In the proposed extraction procedure, a low-density extraction solvent (acetonitrile) was injected into a water sample to form the acetonitrile-water system. A salt (ammonium sulfate) was then injected into the acetonitrile-water solution to separate the system into two phases. The upper organic phase (acetonitrile) was collected and analyzed by HPLC. All the parameters, such as the selection of extraction agent, aqueous two phase formation conditions, ionic strength and pH, are discussed and optimized. The two kinds of compound are linear and in the range of 2.00-400.00 ng/mL, and the correlation coefficient (R²) is greater than 0.999. The detection limits of the method for the compounds ranged from 0.012-0.020 ng/mL and the average recoveries ranged from 94.6%-97.3% with precision of 1.3%-2.5%. Compared with conventional extraction methods, the method has the characteristics of simple operation and rapidity. Pretreatment of environmental water samples can be operated in the field, which is good for the routine analysis of benzo(a)pyrene and benzo(e)pyrene in groundwater.