Disclosed are a method and apparatus for controlling backlight brightness, and a liquid crystal display device, and the method for controlling backlight brightness includes: determining a backlight duty ratio of each backlight zone according to a backlight value of each backlight zone; determining a gain backlight current value of a backlight area according to an average backlight value of the backlight area, and a preset gain curve, wherein each backlight area corresponds to at least one backlight driving chip, and the at least one backlight driving chip controls in parallel more than one backlight zones in the backlight area corresponding to the at least one driving chip; generating a pulse modulation signal of each backlight zone according to the backlight duty ratio of corresponding backlight zone and the gain backlight current value; and adjusting a backlight current of the corresponding backlight zone according to the pulse modulation signal.