Abstract: The OBS length adaptive assembly algorithm can select length thresholds adaptively depending on the input traffic, and make output data bursts length change more slowly than the given length threshold algorithm. But the length thresholds can not be changed by the input self-similar traffic, then it can not depress the self-similarity and packet blocking rate largely. Based on this algorithm, a modified algorithm based on length-changeable thresholds is proposed. The new algorithm can reduce the self-similarity more effectively and adjust the length thresholds according to the properties of the input network traffic stream more adaptively than the length adaptive assembly algorithm. The simulation results show that the packet block rate of the modified adaptive assembly algorithm is only about one tenth of that of adaptive assembly algorithm.