An optical navigation apparatus and an optical navigation method are provided. The optical navigation apparatus includes a light source unit, an image sensing unit, and a processing unit, wherein the processing unit is electrically connected to the light source unit and the image sensing unit. The light source unit generates a beam of light. The image sensing unit captures a plurality of images within a time interval. The processing unit determines that the beam of light is projected onto a touch object according to the images, calculates a piece of displacement information related to the touch object according to the images, generates a comparison result by comparing the piece of displacement information with a threshold, and sets a displacement resolution of the optical navigation apparatus according to the comparison result.