The invention provides a method, device and system for compensating for brightness of a display. The method comprises first acquiring brightness information of at least two pictures to be tested, andclassifying each pixel in the pictures to be tested according to a brightness value; fitting a gray-scale brightness curve of each pixel of each category according to gray-scale values of the picturesto be tested and the brightness value of each pixel; storing a correspondence between a preset coefficient in the gray-scale brightness curve and the position of each pixel in the pictures to be tested; according to a target gray-scale brightness curve, determining current brightness corresponding to the gray-scale values of the pictures to be tested in the position of the pixel where the brightness needs compensation; and determining a corrected gray-scale value according to the current brightness, the position of the pixel where the brightness needs compensation and the gray-scale brightness curve. In the scheme, the byte length of the preset coefficient is smaller than that of the corrected gray-scale value. If the coefficient is 6 bit, the corrected gray-scale value is 8 bit, and thenthe storage space stored in a flash can be reduced by the adoption of the display brightness compensation method, thereby reducing the size of a driving chip.