To provide QoS control for real time traffic in core routers, this paper designs and evaluates a 320 Gb/s switch system, which supports 16 line cards, each operating at OC192c line rate (10 Gb/s). This switch system contains a high performance switch fabric and supports variable-length IP packet interface. These two characters provide advantages over traditional switch fabrics with a cell interface. This switch system supports eight priorities to both unicast and multicast traffic. The highest priority with strict QoS guarantee is for real time traffic, and other seven lower priorities with weighted round-robin (WRR) service discipline are for other common data traffic. Through simulation under multi-priority burst traffic model, we demonstrate this switch system not only can provide excellent performance for real time traffic, but also can efficiently allocate bandwidth among all kinds of traffic. As a result, this switch system can serve as a key node in high-speed networks, and it can also meet the challenge of multimedia traffic to the next generation Internet.