A method for adjusting a gamma curve used in a display control system of a display apparatus, and the method comprises steps of: analyzing each sub pixel gray value distribution of each color in a frame; and adjusting at least a gamma reference voltage according to the sub pixel gray value distribution of the color, such that a gray level voltage number corresponding to the sub pixel gray values in at least a predetermine region which has the relative large statistical number or ratio is increased, and a gray level voltage number corresponding to the sub pixel gray values in at least a predetermine region which has the relative low statistical number or ratio is decreased.