A gate driver and a method for adjusting output channels thereof are provided. The method includes: setting a target number of the output channels; dividing the output channels into a first channel chain and a second channel chain; enabling a scanning operation of the first channel chain according to a clock signal and counting the clock signal to obtain a counting value; and when the counting value reaching a threshold value, enabling a scanning operation of the second channel chain, wherein the threshold value is determined according to a difference value between the target number and the physical number.