The invention relates to a power-gating control method for a graphics processing unit having a unified shader unit, which includes a plurality of shaders. The method includes the steps of: rendering a plurality of previous frames; calculating a first number of active shaders for rendering each previous frame, and a corresponding frame rate of each previous frame; determining a second number of active shaders for rendering a next frame immediately following the previous frame according to the first number of active shaders and the corresponding frame rate of each previous frame; and activating corresponding shaders through one or more power-gating control elements according to the second number of active shaders.