A display apparatus is provided, which includes a display panel and a display controller. The display controller calculates an image average brightness of each image in a video signal from a host. When an absolute difference between a first image average brightness of a current image and a second image average brightness of a previous image is smaller than a predetermined value, the display controller activates a timer to obtain a timer value. When the timer value reaches a first duration, the display controller reduces brightness of each pixel in the current image by a first ratio. When the timer value reaches a second duration, the display controller reduces the brightness of each pixel in the current image by a second ratio. The second duration is longer than the first duration, and the second ratio is higher than the first ratio.