Underwater routing protocols, as a crucial technology for underwater Internet of Things (IoT) communication systems, hold significant research value. However, communication networks in deep-sea environments face challenges such as difficulties in node deployment, high latency, low bandwidth, and energy constraints, necessitating the design of a reliable and efficient routing protocol. Therefore, we propose a Hop-by-Hop Region-Directed Vector Forwarding (HHRDVF) routing protocol. HHRDVF defines a directional forwarding region to constrain node forwarding, effectively avoiding communication link problems caused by network communication voids. At the same time, it enables nodes closer to the destination node to forward data first, thereby improving forwarding efficiency, reducing end-to-end latency, and achieving reliable transmission in underwater communication networks. The simulation results show that the HHRDVF routing protocol can reduce the impact of communication holes in situations where communication nodes are sparse and nodes move slowly.