The design of media access control（ MAC） protocol is one of the key technologies for wireless sensor networks design. SMAC protocol is proposed earlier for the purpose of energy saving of MAC protocol. The working principle of SMAC is briefly described. On the basis of the SMAC

fast collision resolution algorithm is adopted to let the node to fast adjust contention window size according to the channel’s busy

and improve the channel utilization. The Simulation results show that in the case of large network load

the new scheme significantly improved throughput and latency compared with the original protocol SMAC.