Abstract: The existing methods for the determination of trimethylamine in seawater had problems such as large sample amount, expensive instrument, or cumbersome operations, so the research mentioned by the title was conducted. An aliquot (10.00 mL) of seawater sample was taken and placed into a 20 mL-headspace bottle, 2.5 g of sodium chloride, 0.8 g of potassium sulfate, and 2.5 mL of 7.5 mol·L^-1 sodium hydroxide solution were added. The mixture was equilibrated at 85℃ for 40 min. The obtained gas was introduced into the gas chromatograph, and the separation was conducted by heating program on the CP-Volamine quartz capillary column, and trimethylamine was determined by the nitrogen phosphorus detector, with the matrix matching method for quantification. It was shown that linear relationship between values of the mass concentration of trimethylamine and the response signal was kept in the range of 5.0-100.0 μg·L^-1, with detection limit (3.143s) of 0.4 μg·L^-1.The proposed method was applied to the analysis of the spiked blank sample, RSDs (n=5) of the determined values was 2.1%, and recoveries ranged from 92.0% to 118%.