Abstract: n-alkanes, exhibiting stable chemical properties, are ubiquitous in nature. They are favorable indicators of the source of organic matter. Using the gas chromatography-mass spectrometry (GC/MS), this study detected n-alkanes in the surface sediments sampled from the Fangchenggang sea area in September 2021. It analyzed their content and distribution, as well as their source based on characteristic parameters. The results are as follows: ① The n-alkanes of the Fangchenggang sea area manifested a content range of (67.51~850.08)×10^-9 (dw), averaging 476.69×10^-9 (dw), with high values primarily distributed in the southern sea area of Qisha Peninsula; ② They were principally composed of extensive n-C₁₄~n-C₃₅ n-alkane homologues in a bimodal distribution. The former peak group displayed an even-carbon number advantage, while the latter showed an odd-carbon number advantage; ③ The terrestrial-marine alkane ratio (ΣT/ΣM), carbon predominance index (CPI), and terrestrial-marine alkane predominance ratio (TAR) all indicate a significant terrestrial influence on n-alkanes in the Fangchenggang sea area; ④ The average chain length (ACL), alkane index (AI), and Pmar-aq further suggest that n-alkanes were mainly from terrestrial herbs; ⑤ The T-ALK/C₁₆ ratio implies that the Fangchenggang sea area experienced oil pollution; ⑥ The pristane/phytane ratio (Pr/Ph) reveals that n-alkanes in the sediments of the Fangchenggang sea area formed in an oxidizing environment.