The invention provides a method for rapid detection of trimethylamine in an aquatic product, wherein the method includes the specific steps: preparing trimethylamine standard using gases, introducing into an ion mobility spectrometer, successively detecting, to obtain ion mobility spectrum spectrograms of the trimethylamine standard using gases, and thus obtaining a trimethylamine standard curve; introducing top air formed by a to-be-tested aquatic product into an ion mobility spectrum, to obtain an ion mobility spectrum spectrogram of the to-be-tested sample; and comparing the ion mobility spectrum spectrogram of the top air of the to-be-tested aquatic product with the ion mobility spectrum spectrograms of the standard using gases, and calculating the actual content of trimethylamine in the top air of the to-be-tested aquatic product according to the trimethylamine standard curve. The freshness of the aquatic product is characterized by the measured concentration of volatilized trimethylamine through the method, the identification of the freshness degree of the aquatic product can be effectively achieved, good food quality judgment can be provided for consumers, and food safety is ensured.