An optical navigation device has a light-emitting unit, an optical navigation chip and a cover. The light-emitting unit provides a light to a surface of a displacement generating unit. The optical navigation chip has a sensing array, but excludes any optical lens for focusing a reflected light. The sensing array disposed opposite to the surface of the displacement generating unit receives the reflected light which the light provided by the light-emitting unit is reflected from the surface of the displacement generating unit. The cover has a first surface and a second surface, and an angle is formed between the cover and the optical navigation chip, to prevent another reflected light from the surface of the first surface of the cover from entering the sensing array. Particularly, the angle formed between the cover and the optical navigation chip is from 10 degrees to 15 degrees.