The present invention relates to a task scheduling method for a real time operating system (RTOS) mounted to an embedded system, and more particularly, to a task scheduling method which allows a programmer to make a CPU reservation for a task. The task scheduling method for a real time operating system, includes: at a scheduling time point, determining whether or not a highest priority of tasks present in a ready queue is a predetermined value K; if the highest priority is determined to be K, applying a reservation based scheduler to perform a scheduling; and if the highest priority is determined not to be K, applying a priority based scheduler to perform a scheduling; the tasks present in the ready queue, the priority of which is K, contains idle CPU reservation allocation information received as a factor when the tasks the priority of which is K are created.