Disclosed is an externally-adjustable fishing reel drive gear pair backlash adjustment mechanism which includes a drive spindle, a housing consisting of a main cover and a side lid, and a gear pair consisting of a rack and a main gear on the drive spindle; middle portions of the main cover and the side lid being respectively provided with a bearing mounting counterbore, bearings being respectively mounted at two ends of the drive spindle, the drive spindle being mounted in the bearing mounting counterbores of the main cover and the side lid through the bearings at two ends, the bearing of the side lid being bonded to the main gear, a backlash existing between the main gear and the rack; and an adjustment mechanism adjusting a gear pair backlash outside the housing.