The present invention provides a back frame and a backlight system of a flat panel display device. The back frame 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 fixed to the assembling pieces and the bracing piece functions to fix a circuit board. The bracing piece includes a bracing body, a first suspension section, a first bearing section, and a first resilient bent section. The bracing body is fixed to the assembling pieces. The first suspension section extends from the bracing body toward one side of the bracing body. The first bearing section is spaced from the bracing body and extends from the first suspension section toward one side of the first suspension section. The first resilient bent section is located between the first bearing section and the bracing body and is bent from the first suspension section toward one side of the first suspension section. The first bearing section and the first resilient bent section resiliently clamp a first side edge of the circuit board. The technical solution provided by the present invention reduces the manufacturing cost of backlighting display device and also saves the expenditure of mold and overcomes the problem that a circuit board cannot be easily fixed.