提出了一种固定大小帧结构的EPON MAC协议，采用固定的帧长，提高了以太网交换机速率。将一帧周期分成三段，光网络单元不仅报告队列长度信息，而且报告帧到达分布信息，降低了高优先级业务时延抖动，授权采取高优先级优先授权的原则，降低了高优先级业务的接入时延，满足了对时延和时延抖动敏感语音业务的要求。The paper puts forward a EPON MAC of fixed size frame structure.The frame structure of fixed size can improve the the process velocity of exchanger.Frame cycle is divided into three segments,ONU not only reports the queue size,but also reports the distribution of frame arrival,Which will decrease the delay jitter of high priority traffic.We adopt the principle of first grant of high priority traffic,this can decrease the access delay of high priority traffic. All can satisfy the requests of real-time voice traffic which is sensitive to the delay and delay jitter.