In this paper, a Guard Channel (GC) scheme based on dynamic thresholds is proposed. It keeps the ratio of new connection blocking probability to handoff connection blocking probability to a predefined value, which guarantees the priority and fairness among connections. At the same time, it optimizes and improves the performance metrics for handoff: new connection blocking probability and handoff connection blocking probability and system utilization. In addition, the algorithm adopts self-adjusting to be adaptive to varying traffic loads and makes the blocking probability smoother. Lastly the results by analysis and simulation prove the feasibility of this scheme.