Abstract: The target compound in the sample was converted into pentachlorophenol (PCP) in the presence of sulfuric acid (1+1) solution. The solution after extraction was purified on activated HLB solid phase extraction column, and then pentachlorphenylacetate (PCP-OAc) was derived from the reaction of PCP with acetic anhydride in the presence of potassium carbonate solution. The solution after extraction was separated by GC using TR-5MS capillary column as stationary phase. NCI and SRM were adopted in MS, and internal standard method was used for quantification. Linear relationship between values of peak area ratio and mass concentration of PCP was found in the range of 0.20-20.0 μg·L^-1, with detection limit (3S/N) of 1.0 μg·kg^-1. The blank samples of crab and codfish were used as matrix, and test for recovery was made by standard addition method, giving results in the range of 78.0%-104%, with RSDs (n=6) ranged from 2.0% to 12%.