Medium access control(MAC) directly effects the energy efficicy and the real-time in wireless sensor network. This paper studies the state of the art of current real-time MAC protocols, and then introduces a distributed medium access control protocol that provides multiple priority levels. The channel is accessed by stations according to their priorities, and for stations with the same priority, frames are sent in a round manner. The fairness between different priorities is provided. The datum with higher priority can be sent in the real time. So the protocol guarantees lower energy consume and lower time
delay. The Simulation and experiment results indicate that the protocol provides high channel utilization and bounded delays for real-time frames, and can be applied in the many fields.