A backlight brightness control method and a backlight brightness control device are provided. The backlight brightness control method includes: acquiring a luminous brightness value of a display panel; determining a relationship between the luminous brightness value and a preset brightness value by a brightness control circuit; transmitting an adjusted current value to a backlight driver module according to the relationship by the brightness control circuit; and generating a current having the adjusted current value by the backlight driver module to drive a backlight module in the display panel to emit light.