Provided are a small low power embedded system and a preemption avoidance method thereof. A method for avoiding preemption in a small low power embedded system includes fetching and running a periodic atomic task from a periodic run queue, reducing any one of periodic atomic tasks or performing the change of a task after changing a field of the run periodic atomic task into a run standby state, according to a result value of the run of the periodic atomic task, fetching a sporadic atomic task from a sporadic run queue, and acquiring a system clock, running the fetched sporadic atomic task according to run time in the worst condition, and reducing any one of sporadic atomic tasks or performing the change of an event after a field of the run sporadic atomic task into a run standby state, according to a result value of the run of the sporadic atomic task.