The existing Terahertz wireless personal area network dual-channel Media Access Control (MAC) protocol works in WiFi channel and Terahertz channel. Due to the great difference in frequency between the two channels, the coverage of omnidirectional antenna and directional antenna is different, which will greatly reduce the success rate of message transmission among nodes and the throughput of the network as a whole. In addition, in the existing dual-channel MAC protocol of Terahertz wireless personal area network, there is some redundant control overhead, which leads to low channel utilization. This paper proposes a High Efficient Dual-Channel MAC Protocol Based on Relay （HE-BRMAC）in Terahertz wireless personal area network. The HE-BRMAC is divided into relay auxiliary mechanism and adaptive control cost reduction mechanism. Through adaptive control cost reduction mechanism, the control frame is more compact. In this way, the success rate of message transmission can be improved, and the overall throughput of the network can be improved. Moreover, the control overhead can be reduced, and the channel utilization can be improved. It is noted that when the number of nodes is large, HE-BRMAC has more significant effect.