Ethernet passive optical network (EPON) is a promising local subscribe access architecture that combines low cost point-to-multipoint passive optical network with Ethernet. One of the key problems in EPON is how to allocate the upstream bandwidth effectively. In the paper we present a dynamic bandwidth allocation scheme that will incorporates the priority operation into medium access control (MAC) protocol design to achieve quality of service (QoS) for subscribers. The scheme minimizes packet delay and delay variation for high priority traffic to ensure Qos through introducing a fixed cycle time. Simulation result proves that.