A method for determining a rebooting action of a computer system includes: a keyboard controller of the computer system detecting whether a signal representing a system stage transformation is transmitted from a south bridge chipset; determining whether a system status flag is set as “ON” when the signal representing the system stage transformation is received by the keyboard controller; setting a rebooting flag as “ON” and setting the system status flag as “OFF”; determining whether a system sleeping flag representing the computer system isn't activated is “ON” and determining whether the rebooting flag is set as “OFF” according to this determined result; detecting whether the signal representing the system stage transformation is transmitted from the south bridge chipset; determining whether the rebooting flag is set as “ON”; and determining whether the computer system executes the rebooting action according to a determined result of whether the rebooting flag is “ON”.