An operating method of a base station for changing a fixed resource allocation to reduce overhead in a mobile communication system includes calculating a total amount of resources allocated to a corresponding subframe in a period of a corresponding fixed allocation resource; when the total amount of the resources allocated to the corresponding subframe is greater than a threshold, temporarily canceling one or more corresponding fixed allocation resources to make the total amount of the resources allocated to the corresponding subframe less than or equal to the threshold; and reallocating the one or more canceled fixed allocation resources according to a corresponding rule.