In Terahertz wireless local area networks, to fulfill the request of data transmission efficiency, a superframe structure of medium access control (MAC) protocol is proposed. Based on the proposed superframe structure, three optimization mechanisms are further proposed, which are dynamically adjusting the length of contention access period, slots distribution without further sending slots requests and deleting redundancy control bits. By applying the network simulator software OPNET, the performance of the proposed optimized MAC protocol is compared with the existed highthroughput lowdelay MAC (HLMAC)〖JP〗 protocol as well as the standard IEEE 802.15.3c protocol. From the perspective of network throughput, the proposed optimized MAC protocol is about 3.45% and 11.11% better than the HLMAC protocol and the standard protocol. In the view point of average access delay, around 28% and 50% improvements are obtained. And the probability of data frame transmission gains about 3.3% and 10.6% than that of the HLMAC and the standard protocol.