The present invention provides a distributed cluster processing system and a packet processing method thereof. The system includes at least one external interface unit, multiple processing units, and a switching unit, where each of the at least one external interface unit is connected between a corresponding processing unit of the multiple processing units and an external network element, and is configured to receive a packet from the external network element, forward the packet to a corresponding processing unit of the multiple directly connected processing units, and send a processed packet to the external network element; and each of the multiple processing units performs specified service processing and is respectively connected to the switching unit, so that the multiple processing units and the switching unit form a star topology structure. According to the system and the method, through a logical combination between the processing units, end-to-end high performance may be achieved.