Fluorescent test paper for detecting mercury ions is firstly prepared, the fluorescent test paper including a fluorescence development area and a standard fluorescent colorimetric card. With reference to an excited color corresponding to a reference channel in the standard colorimetric card, the color corresponding to a carbon quantum dots distribution area on the fluorescent test paper is observed to check the fluorescence detection environment during detection with the fluorescent test paper. In colorimetric detection of the content of mercury ions, the concentration of Hg2+ is detected based on an excited color, in the standard colorimetric card, that corresponds to a standard mercury ion sample and is closest to a color signal in a copper nanoclusters distribution area on the fluorescent test paper.