An apparatus and a method for optimizing a satellite system considering a hard error stability and a soft error stability are disclosed. The satellite system optimizing method which considers a hard error stability and a soft error stability according to an exemplary embodiment of the present disclosure includes acquiring hardware information of a processor which is loaded in the satellite system; acquiring workload information including a task which is performed by the processor; establishing a scheduling policy for the task based on the hardware information and the workload information; and quantifying a soft error stability and a hard error stability in accordance with the scheduling policy.