A digital diagnostic system, comprising: a host which comprises: an image capture module, for capturing a reflected light from an affected part to form an image; a display module, for displaying the image captured by the image capture module; a processing unit electrically connected to the image capture module and the display module, for processing the image and displaying the image on the display module; a focus adjustment module, for driving the image capture module to linearly move along an image capturing direction; a plurality of first conductive contacts; an adapter arranged in front of the image capture module; and a power module, for supplying power to the digital diagnostic system in operation; and at least one optical lens module (20a, 20b, 20c, 20d, 20e) detachably connected to the adapter, wherein the optical lens module (20a, 20b, 20c, 20d, 20e) comprises: a plurality of optical lenses having a plurality of curved surfaces, for converging the reflected light on the image capture module; a light source positioned off an optical axis of the optical lens, for providing illumination light to illuminate the affected part; and a plurality of second conductive contacts, for electrically connecting to the corresponding first conductive contacts to supply power to the light source when the optical lens module (20a, 20b, 20c, 20d, 20e) is connected to the adapter. a host which comprises: an image capture module, for capturing a reflected light from an affected part to form an image; a display module, for displaying the image captured by the image capture module; a processing unit electrically connected to the image capture module and the display module, for processing the image and displaying the image on the display module; a focus adjustment module, for driving the image capture module to linearly move along an image capturing direction; a plurality of first conductive contacts; an adapter arranged in front of the image capture module; and a power module, for supplying power to the digital diagnostic system in operation; and an image capture module, for capturing a reflected light from an affected part to form an image; a display module, for displaying the image captured by the image capture module; a processing unit electrically connected to the image capture module and the display module, for processing the image and displaying the image on the display module; a focus adjustment module, for driving the image capture module to linearly move along an image capturing direction; a plurality of first conductive contacts; an adapter arranged in front of the image capture module; and a power module, for supplying power to the digital diagnostic system in operation; and at least one optical lens module (20a, 20b, 20c, 20d, 20e) detachably connected to the adapter, wherein the optical lens module (20a, 20b, 20c, 20d, 20e) comprises: a plurality of optical lenses having a plurality of curved surfaces, for converging the reflected light on the image capture module; a light source positioned off an optical axis of the optical lens, for providing illumination light to illuminate the affected part; and a plurality of second conductive contacts, for electrically connecting to the corresponding first conductive contacts to supply power to the light source when the optical lens module (20a, 20b, 20c, 20d, 20e) is connected to the adapter. a plurality of optical lenses having a plurality of curved surfaces, for converging the reflected light on the image capture module; a light source positioned off an optical axis of the optical lens, for providing illumination light to illuminate the affected part; and a plurality of second conductive contacts, for electrically connecting to the corresponding first conductive contacts to supply power to the light source when the optical lens module (20a, 20b, 20c, 20d, 20e) is connected to the adapter.