A power-managing key apparatus uses a power key to integrate the function of ACPI management of computer hardware and hibernation on/off of operation system. A processor coupled to the power key detects pressing-time parameters of the power key and a current state of the computer. The processor sends a hardware signal to emulate ACPI power button function in order to power on/off computer and awake the computer from a power saving mode. The processor sends a software signal to an operation system of the computer to disable/enable a hibernation state. Therefore, the complicated power management performed by computer hardware and operation system can be simplified.