The present invention provides a back frame of flat panel display device, which includes at least first and second primary assembling pieces, in which the first primary assembling piece has an end forming at least two joint sections, and each of the joint sections has a structure mating an end of the second primary assembling piece. The first primary assembling piece uses one of the joint sections to join the corresponding end of the second primary assembling piece. The present invention also provides a mold for making a back frame of flat panel display device, a method for manufacturing a back frame of flat panel display device, and a backlight system. The back frame mold of the back frame, the mold for back frame, the method for manufacturing back frame, and the backlight system is of a simple structure and can reduce the expenditure of the back frame mold, and can also save the material used for back frame so as to lower down the cost of flat panel display device.