1. A task scheduling method for a real time operating system, comprising: 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, wherein the applying a reservation based scheduler to perform the scheduling comprises: determining whether or not the tasks, the priority of which is K, have idle CPU reservation allocation information; and performing the scheduling of tasks having the idle CPU reservation allocation information and the scheduling of tasks not having the idle CPU reservation allocation information in sequence, wherein the applying a reservation based scheduler to perform the scheduling comprises: when a round time is not set, setting a time for a first round; setting the tasks, the priority of which is K, to a set T CPU of tasks having the idle CPU reservation allocation information and a set T G of tasks not having the idle CPU reservation allocation information; and allocating an idle CPU to tasks pertaining to the set T CPU , and allocating the idle CPU to tasks pertaining to the set T G , wherein the idle CPU is a percentage of the left CPU time usable by the tasks, the priority of which is K, except for the CPU occupancy rate of the task, the priority of which is higher than K.