Disclosed is a windows-based power management method for optimally distributing power for various tasks in a portable device. The power management method includes the following steps: (a) categorizing each task to be executed by the portable device, (b) prescribing a power management policy, (c) distributing shares of a power supply unit among the tasks based on the category the tasks are associated therewith according to the power management policy, and (d) in response to the commands input by the user through a graphical user interface, increasing the share of the power supply unit provided for a task running within an active window of the portable device to accomplish an optimized distribution of power among tasks to be executed by the portable device.