A light mixing element in a shape of a prism, and a cylinder of the prism of the light mixing element includes a first light-emitting inclined surface, a second light-emitting inclined surface, a bottom surface, a incident surface and a reflecting inclined surface; one side of the second light-emitting inclined surface is connected with one side of the first light-emitting inclined surface to form a top angle; the bottom surface is arranged opposite to the top angle; the incident surface is connected between one side of the bottom surface and the other side of the first light-emitting inclined surface; and the reflecting inclined surface is connected between the other side of the bottom surface and the other side of the second light-emitting inclined surface and arranged opposite to the incident surface and the first light-emitting inclined surface.