Compared to other multiple access protocols, statistical priority-based multiple access protocol (SPMA), which can be applied to long-range, high-speed, large-capacity communication system, plays an important role in the research of wireless communication. However, since SPMA claims that the channel occupancy statistic must be uploaded from the physical layer in real time, it will increase the difficulty of the application implement. This paper proposes a novel improved algorithm based on the channel occupancy statistic, which does not need the physical layer statistics. Meanwhile, the threshold setting is one of the key issues in SPMA protocol, but most current literature do not provide an effective method about threshold setting. An algorithm of threshold setting is also discussed in this paper. By theoretical analysis and simulation, it can be proved that our proposed algorithm can simultaneously guarantee high one-hop first-time success rate and low delay for high-priority packets.