The spectrum allocation in elastic optical network(EON) needs to meet the spectrum consistency and continuity constraints of subcarriers at the same time. The spectrum fragments of different sizes will be generated after the allocation or release of services with different bandwidth requirements, which will affect the allocation of subsequent services and the utilization of spectrum resources. An improved EON defragmentation algorithm based on resource saving strategy(RSS) is proposed. In the process of defragmentation, the number of continuously available frequency gaps and the number of frequency gaps needed for arriving services can be as equal as possible to avoid the generation of new spectrum fragments. Theoretical analysis and simulation results show that in 100~ 600 Erl, compared with the traditional defragmentation algorithm, the improved algorithm can reduce the bandwidth blocking rate by 8.54%.