The bandwidth allocation problem in the next generation passive optical network(NG-PON2) is one of the research hotspots. Aiming at the problem of how to reasonably allocate bandwidth resources according to the changing state of the network in the dynamic network environment, a dynamic bandwidth allocation algorithm based on statistical periodic quality of service(SPSQ) with adaptive ability is proposed. Combined with the characteristics of the periodic demand of network resources, the dynamic bandwidth allocation problem in passive optical networks is analyzed by statistical method. The simulation results show that the algorithm can adapt to the data transmission of the network and improve the quality of service of the network when the traffic changes.