A power saving method includes enabling an input signal detection unit of the display controller for detecting a first presence of at least one input signal of the display controller, entering the display controller to a power-off mode temporarily for decreasing an operation power from a first power to a second power within a second time period when the at least one input signal is not received by the input signal detection unit within a first time period, detecting a second presence of the at least one input signal continuously by the input signal detection unit after the second time period elapses, and adjusting an operation mode of the display controller according to the second presence of the at least one input signal. The second power is smaller than the first power. The second power corresponds to a power of the display controller under the power-off mode.