The present application provides a method for controlling a backlight source, a device for controlling a backlight source and a liquid crystal display, where the method includes: determining time intervals of received synchronous signals; determining an output delay compensation value of the synchronous signals, according to the time intervals and fixed response delay time for processing the synchronous signals; generating a compensated synchronous signal according to the output delay compensation value of the synchronous signals; transmitting the compensated synchronous signal to a PWM driver. The application allows a backlight source to perform optical display according to multipath control signals with relatively stable frequency, and reduces backlight blinking of the backlight source.