The present invention provides a back frame of a flat panel display device, which includes at least two assembling pieces. The at least two assembling pieces are joined to form the back frame. The back frame further includes a bracing piece. An end of the bracing piece is fixed to the assembling piece and an opposite end of the bracing piece suspends. The present invention also provides a backlight system of flat panel display device. With this arrangement, the back frame and the backlight system of the flat panel display device of the present invention have a mold for the back frame is of a simple structure, the cost of back frame mold is reduced, the material used for back frame is saved, and the manufacturing cost of flat panel display device is lowered down. Further, the bracing piece has an end fixed to the assembling piece and an opposite end suspending so that the structure of the back frame is simple, the material for the back frame is saved, and thus, the weight and cost of the flat panel display device are reduced.