The invention discloses fluorescent hydrogel and a low-temperature in-situ preparation method and application thereof. According to the fluorescent hydrogel and the low-temperature in-situ preparationmethod and application thereof, amino-containing small organic molecules, citric acid, a polymerizable monomer and a cross-linking agent are taken as raw materials, and a cross-linked hydrogel body is formed at a lower temperature; and in the forming process of the hydrogel body, the amino-containing small organic molecules are oxidized in a polymer network for in-situ reaction to form a luminescent substance, the acidity is adjusted through the citric acid, and the fluorescent hydrogel with a good fluorescence effect is obtained by one step.