The invention discloses a quick detecting method for formaldehyde content in an aquatic product. The quick detecting method comprises the following steps: (1) preparing a Schiff reagent; (2) making a standard color chart, namely respectively adding 5mL formaldehyde solutions with different concentrations to 8 different colorimetric tubes, respectively adding a 0.5mL Schiff reagent to the colorimetric tubes, adjusting the pH of the solutions to 2.5, shaking up the solutions, stewing and developing for 10 minutes, and making the color chart by taking colors displayed by the solutions as standard colors; and (3) detecting, namely extracting a 5mL soak solution of an aquatic product sample to be detected, adding a 0.5mL Schiff reagent to the soak solution, adjusting the pH of the solution to 2.5, shaking up the solution, stewing and developing for 10 minutes, and comparing the color displayed by the solution with standard colorimetric splines. The quick detecting method disclosed by the invention has the characteristic that the formaldehyde and the Schiff reagent react at a normal state to generate a purple-red compound, and the shade of the compound is in direct proportion to formaldehyde content so as to realize colorimetric assay. The quick detecting method has the advantages of simple and quick operation, high sensitivity, simple conditions, low reagent price, and the like.