A GC-MS method was established for the determination of 9 polychlorinated naphthalenes(PCNs),including 1-chloronaphthalene,2-chloronaphthalene,1,4-dichloronaphthalene,1,2,3,4-tetrachloronaphthalene,1,3,5,7-tetrachloronaphthalene,1,2,3,5,7-pentachloronaphthalene,1,2,3,5,6,7-hexahydropyrrolizinium,1,2,3,4,5,6,7-heptachloronaphthalene and octachloronaphthalene in groundwater.Comparative study was conducted between the liquid-liquid extraction(LLE) and solid phase extraction(SPE) for extraction of 9 PCNs in groundwater,and LLE was selected as sample preparing method as it has higher extraction efficiency than SPE.The calibration curves of 9 PCNs were linear in the range of 5-100 μg/L with correlation coefficients(r) more than 0.995.The spiked recoveries for groundwater samples ranged from 70.7% to 112% with relative standard deviations(RSD，n=5) less than 9.9%,and the method detection limits(S/N=3) were in the range of 4.21-7.41 ng/L.The method was accurate and sensitive,and was successfully applied in the determination of 9 PCNs in real groundwater sample.