A power management method for a computer system is provided. The power management method includes: obtaining a system power consumption; determining whether the system power consumption is greater than a first safe operating point; when the system power consumption is greater than the first safe operating point, controlling a CPU and a graphics processing unit (GPU) to activate a frequency reduction mechanism according to a first adjustment sequence; when the system power consumption is not greater than the first safe operating point, determining whether the system power consumption is smaller than a second safe operating point; and when the system power consumption is smaller than the second safe operating point, controlling the CPU and the GPU to deactivate the frequency reduction mechanism according to a second adjustment sequence. The second adjustment sequence is reverse to the first adjustment sequence.