Abstract: Dynamic bandwidth allocation of the uplink is a hot technique in EPON system. By analyzing the merits and weaknesses of the existing algorithms, a novel dynamic bandwidth allocation algorithm is proposed, which supports differentiating service levels and guarantees the quality of the service. The new algorithm determines the polling cycle, allocates the requested bandwidth to high-priority services, and allocates bandwidth to middle and low priority sevices by weight. It also takes the reallocation of the excess bandwidth into account. Simulation results show that this scheme can meet the bandwidth need of high priority service while taking low priority service into account. The algorithm makes the distribution of system bandwidth more rational and improves the efficiency of up-link bandwidth and the quality of service.