The invention relates to a method for determining the 2,4,6-tribromophenol content of sea water and fresh water, which comprises the following steps: extracting a sample with normal hexane under an acidic condition (pH is less than 2), drying a resulting extract and concentrating the resulting extract, derivatizing the resulting concentrate with aceticanhydride in an alkaline environment (pH is between 10.5 and 11.5), and analyzing the resulting derivative by using an ECD detector; weighting a standard 2,4,6-tribromophenol, dissolving the standard 2,4,6-tribromophenol in solution of normal hexane, adjusting the volume of the solution, using the solution as stock solution, and adding 4,4- dibromooctafluorobiphenyl (internal standard) into the stock solution; diluting the standard stock solution with 2,4-dichlorobenzoic acid (substitute) to obtain a standard solution for use with concentration gradient; derivatizing the standard solution for use with aceticanhydride, and testing the sample by using a gas chromatograph ECD detector; and finally, obtaining a result through calculation. The method for detecting the 2,4,6-tribromophenol content of sea water and fresh water has the advantages of high speed, effectiveness, detection limit of 0.01 ug/L and error rate no more than 10 percent. Therefore, the method is a reliable and easy-to-implement method for detecting the 2,4,6-tribromophenol content of sea water and fresh water and can satisfy demands of searches and production.