A method for dynamically adjusting fluorescent imaging is provided. The method is used in a device and includes the following steps: emitting, by a light emitting diode, light to illuminate teeth in an oral cavity, wherein the light is used to generate fluorescence from the teeth; filtering, by an optical filter, the fluorescence; receiving, by an image sensor, a signal and adjusting a gain value of an analog-to-digital converter according to the signal; converting, by the analog-to-digital converter, the filtered fluorescence into a digital signal and adjusting the digital signal according to the gain value; and generating, by a processor, an output image signal that corresponds to the gain value from the digital signal.