An image-processing method for marking plaque fluorescent reaction areas is provided, including: obtaining a first RGB image of a mouth region; obtaining a second RGB image of the mouth region; respectively converting the first RGB image and the second RGB image into a first HSV image and a second HSV image; obtaining a first average brightness value of the first HSV image and a second average brightness value of the second HSV image; normalizing the first average brightness value or the second average brightness value according the first average brightness value and the second average brightness value to obtain a normalized image; converting the normalized image into a third RGB image, and obtaining a plurality of pixel points of the dental plaque according to the third RGB image and the first RGB image or the second RGB image; and marking the pixel points in the third RGB image.