Abstract: Investigation on the diffusion trend of pollutants at the sediment-water interface is very valuable for their environmental risk assessment.Based on concentrations of perfluoroalkyl compounds (PFASs) in seawater and sediment samples from the Dalian bay, the diffusion trend of PFASs at the sediment-water interface and the spatial variability of PFASs were investigated by using the fugacity fraction (ff) and the coefficient of variation (C_v), respectively.Furthermore, the effect of organic carbon content on the diffusion trend was analyzed with the response coefficient (RC).The results show that the total concentration of 9 PFASs in seawater and sediments of Dalian Bay is moderately variable.The variation of concentration in the sediment was slightly larger, which might be affected by historical pollutants and pollution accidents.During the diffusion process at the sediment-water interface, the perfluoroalkyl sulfonic acids and perfluoroalkyl carboxylic acids exhibited the similar diffusion characteristics that was the ff value gradually decreased with increasing chain length of PFASs.Short-chain PFASs tended to exist in seawater of the Dalian bay, while the long-chain PFASs tended to diffuse into sediments.The organic carbon content is an important parameter affecting the diffusion trend of PFASs at the sediment-water interface, and the effect on long-chain PFASs was more obvious than that on short-chain PFASs.As a kind of persistent organic pollutant, PFOS is mainly in equilibrium at present in the Dalian bay.