The present invention provides a flat panel display device, which includes a backlight system and a display panel. The backlight system includes a light source, a light homogenization mechanism, and a back frame. The back frame carries the light source and the light homogenization mechanism, and the light homogenization mechanism guides light from the light source into the display panel. The back frame includes primary assembling pieces, secondary assembling pieces, and a bracing piece for fixing a circuit board. The at least two primary assembling pieces are connected through joining and the two primary assembling pieces use different thermally conductive materials. Further, the primary assembling piece includes a joint section that forms a reinforcement structure and a circuit board is mountable and position adjustable through a bracing piece. The present invention also provides a stereoscopic display device and a plasma display device. The back frame and the backlight system of the present invention have a back frame of simple structure, reduce the expenditure of a back frame mold, facilitate heat dissipation, allow strength of the back frame to meet a desired requirement, improve fixing of circuit board, and save the material used for back frame so as to lower down the manufacturing cost of flat panel display device.