A detachable projection device, a sealing housing thereof, and a wearable apparatus are provided. The sealing housing includes a first cover, a second cover, a first waterproof and dustproof gasket having an enclosed loop-shape, and a transparent case. The first cover and the second cover respectively have two sealing edge portions corresponding in shape to each other. The second cover is detachably fastened to the first cover, and the first waterproof and dustproof gasket is gaplessly sandwiched between and abutted against the two sealing edge portions, so that the first cover, the second cover, and the first waterproof and dustproof gasket jointly define an accommodating space. The transparent case is connected to the second cover and has an insertion slot that is in spatial communication with an optical area of the accommodating space.