An apparatus and method for scheduling requests to a source device is provided. The apparatus comprises a high-priority request queue for storing a plurality of high-priority requests to the source device; a low-priority request queue for storing a low-priority request to the source device, wherein a priority of one of the high-priority requests is higher than the priority of the low-priority request; a history counter for storing an information related to at least one requesting interval between two adjacent high-priority requests; and a scheduling module for scheduling the high-priority requests and the low-priority request according to the information.