Embodiments of the present invention provide a liquid crystal display device and a manufacturing method thereof. The device comprises: an upper substrate, comprising: substrate; a color filter and a black matrix, formed on a surface of the substrate facing a lower substrate in the same layer; a lower substrate, cell-assembled with the upper substrate and comprising: a base substrate; a gate metal bus, a gate insulating layer, a source/drain metal bus and a first insulating protection layer, which are formed on the base substrate sequentially; a transparent electrode, formed on the first insulating protection layer; and a second insulating protection layer, covering the transparent electrode; and a seal agent, provided at a periphery of a display area of the liquid crystal display device, wherein an upper portion of the seal agent is attached to the substrate and a lower portion thereof is attached to the second insulating protection layer.