In order to solve the problem of holding-time-aware routing and spectrum allocation (HTA-RSA) in software defined elastic optical networks (SD-EON), multi-path routing (MPR), traffic grooming (TG), and adaptive modulation (AM) are combined to establish an integer linear programming model with the optimization objective of minimizing the spectrum resource occupation, and a holding-time aware multipath routing and spectrum allocation (HMRSA-TG) algorithm based on TG is proposed. For both immediate reservation allocation (IR) and advance reservation allocation (AR), the single path single service allocation method is used to establish the service connection. If it fails, the single path multi sub service allocation method is used. If it is still unsuccessful, the multipath multi sub service allocation mode is tried. In order to minimize the spectrum resource occupation and release the spectrum resource as soon as possible, when establishing the service connection, the allocation method with the least spectrum resource is preferred. When the spectrum resources are the same, the allocation method with the minimum total occupied time slots is preferred. Simulation results show that this algorithm can reduce the blocking rate and improve the spectrum utilization.