Software-defined network (SDN) is a new networking paradigm, which separates the control plane and data plane, for the implementation of flexible networking. However, few papers focus on the mobility management issue in SDN networks. For filling this part, we propose a SDN-based trajectory-aware seamless handover (STASH) scheme in ultra-dense smallcell networks. In STASH, the SDN controller will preset the flow entries of switches according to UE’s trajectory information for reducing the signaling overhead and use a multiple pre-registration mechanism to mitigate the workload of the SDN controller. Moreover, our scheme improves the throughput and reduces the handover latency by multiple antennas. The simulation results show that our scheme outperforms other existing schemes in terms of handover latency and network throughput.