A system for driving a lamp module (13) includes a converter (11), a driving circuit (12), and a pulse width modulation (PWM) controller (14). The lamp module includes a plurality of lamps. The converter converts a received voltage to a direct current (DC) voltage. The driving circuit converts the DC voltage to an alternating current (AC) voltage. The PWM controller is connected between the converter and the lamp module, for regulating the DC voltages outputted from the converter according to current flowing through the lamps of the lamp module. In one embodiment, the system includes a bus inverter controller. The bus inverter controller is connected between the driving circuit and the lamp module, for regulating a working frequency thereof and controlling the AC voltage outputted from the driving circuit when the lamps are turned on. The system has a reduced number of PWM controllers and a relatively low cost.