A backlight module control system includes a plurality of backlight sub-modules, a control signals output unit, a voltage converter and a plurality of current control units. The control signals output circuit is for providing a voltage control signal, a current control signal and a plurality of PWM signals; the voltage converter is coupled to the control signals output circuit and the backlight sub-modules, and is for outputting an output voltage to the backlight sub-modules according to the voltage control signal; the current control units are coupled to the backlight sub-modules, respectively, and each current control unit is for determining a current of its corresponding backlight sub-module according to the current control signal, and each current control unit is further utilized for determining whether its corresponding backlight sub-module is enabled or not according to its corresponding PWM signal. In addition, only one backlight module is enabled at a same time.