With the continuous advancement of substation intelligence, communication network traffic within substations has surged. Strict real-time requirements associated with primary equipment operations present new challenges for comprehensive traffic scheduling. TSN(time-sensitive networking) technology, which ensures the high reliability and low latency transmission demands of substations, has gained significant attention in recent years. The issue of effective bandwidth resource utilization within the "protection band" of the HOLD & RELEASE mechanism in TSN technology was addressed. The frame transmission conditions within the "protection band" were redefined, leading to the proposal of an improved HOLD & RELEASE mechanism to achieve dynamic utilization of bandwidth resources. The implementation process of the improved HOLD & RELEASE mechanism was outlined in conjunction with the IEEE Std 802.3br-2016 standard. The feasibility and effectiveness of the proposed algorithm are verified through simulation examples. The simulation results demonstrate that the improved HOLD & RELEASE mechanism significantly enhances the bandwidth utilization of substation communication networks without incurring any additional overhead.