Display device and assembling method of display device

A display device is provided and comprises a middle frame, the middle frame comprises a top side frame, a left side frame and a right side frame; the left side frame and the right side frame are connected to the two opposite ends of the top side frame respectively and formed by extending the top side frame towards the same direction, the top side frame, the left side frame and the right side framejointly form a containing space in a surrounding mode, a sliding groove is formed in the inner side of the middle frame, and the sliding groove is communicated with the containing space; the connecting piece is arranged in the sliding groove; the back plate is contained in the sliding groove in a sliding mode and can slide into the containing space along the sliding groove; the optical assembly is fixed on the connecting piece; the display panel is fixed to the outer side of the middle frame and located on the side, away from the backboard, of the optical assembly, and a ground side frame ismounted at the end parts,