In order to solve the problem of excessive spectrum fragmentation in elastic optical networks, this paper proposes an odd-even partition spectrum assignment algorithm based on holding time. The algorithm considers the factors such as the mixed line rate services and the holding time for services, according to the different types of services in the link, the special area is divided into two types: odd and even, which makes the adjacent odd and even areas form a shared area and improves the success rate of service transmission. Combined with the holding time of the services, a partition-time combine strategy is adopted to effectively reduce the spectrum fragmentation in the time domain. The simulation results show that the algorithm can effectively reduce the bandwidth blocking probability and improve the spectrum utilization ratio.