IEEE 802.16 is defining standards for Mobile Multihop Relay (MMR). The major purpose of MMR is to efficiently extend the coverage of a BS and to enhance the system throughput. Relay Station (RS) has been introduced to fulfill this goal. However, packets in MMR would have a large probability of failure transmission because not all links over the multihop path are in good channel condition. Therefore, Hybrid Automatic Repeat reQuest (HARQ) has been designed to increase the reliability in multihop transmission. However, the retransmission mechanism proposed in 802.16j is not efficient. It will result in high packet delay. In this paper, we propose Dynamic Pre-allocation HARQ (DP-HARQ) which pre-allocates bandwidth for HARQ. Therefore, the packet delay is reduced significantly. The pre-allocated bandwidth is dynamically adjusted so the channel utilization will not be degraded much. We also propose mathematical models to analyze the proposed DP-HARQ. The analysis is validated by extensive simulations. Results show that the proposed DP-HARQ can reduce packet delay and jitter significantly.