The invention discloses a method and a device for controlling backlight during entering or quitting a wide-screen film display mode. The method comprises the steps of determining the first backlight state of a backlight subarea in a display screen when an image to be displayed is displayed on the display screen, determining whether the first backlight state of the backlight subarea is the same with a second backlight state of the backlight subarea when an image one frame prior to the image to the displayed is displayed, and if the first backlight state is different from the second backlight state, setting the backlight luminance value of the backlight subarea according to the first backlight state and the second backlight state so that the backlight luminance value monotonously changes when continuous N frames of images starting from the image to be displayed are displayed in the backlight subarea, wherein N is a positive integer greater than 0. The method for controlling the backlight during entering or quitting the wide-screen film display mode is capable of avoiding backlight blinking occurring when the backlight states are switched a plurality of times.