A light emitting diode (LED) back light system and a method for driving a back light source used therein are provided. The LED back light system includes an LED back light source, a power converting circuit, and a sequential outputting circuit. The LED back light source includes a plurality of areas. The power converting circuit is used to convert an external power source into a driving power source. The sequential outputting circuit is electrically connected to the power converting circuit and said areas so as to generate a plurality of driving signals according to the driving power source. In addition, said driving signals are sequentially outputted to drive said areas at different time.