A frequency synchronization device for a large LCD having a plurality of lamps as a background light source is disclosed. The device comprises a power amplification unit arranged in loop, each power amplification unit being electrically coupled to one of the lamps, adapted to generate a synchronous signal, and adapted to send the synchronous signal to the coupled lamp for causing the lamps to operate at the same frequency; a plurality of current sampling elements each electrically coupled to one of the lamps for sampling current thereof; and control means comprising a control element and a diode, the control means being electrically coupled to current sampling elements so as to stabilize the current of the lamps. The connection and circuitry of the device are much simplified and improved.