The invention provides a polaroid which comprises a polaroid body, at least one corner of the polaroid body is provided with a notch, when the polaroid is attached to a substrate of a liquid crystal display panel, the substrate exposes an area corresponding to the at least one notch, the notch is provided with an inner side edge and an outer side edge which are opposite to each other, and the inner side edge and the outer side edge have at least three intersection points. According to the polaroid, under the condition that it is guaranteed that the protective film of the polaroid is easy to tear, the notch in the polaroid is designed to be the non-communication area, compared with a crescent-shaped notch in the prior art, the notch is smaller, and the area exposed out of the substrate is reduced. After the liquid crystal display panel is attached to the backlight module, the gap between the liquid crystal display panel and the backlight module is reduced, so that the attaching area between the polaroid and the backlight module can be enlarged, the adhesive force between the polaroid and the backlight module is increased, the stripping risk is reduced, and the yield of the liquid crystal display device is improved. The invention further provides a liquid crystal display panel, a liquid crystal display device and an assembling method thereof.