This　paper　first　analyzes　the　delay　and　energy　consumption　mechanism　of　SMAC.　Then　it　proposes　an　improved　DC-SMAC　protocol　by　replacing　the　fixed　duty　mechanism　with　adaptive　duty　cycle　mechanism,　which　adopts　a　priority　discriminant　function　to　make　the　node　with　more　packets　have　the　priority　to　access　channel.　The　simulation　results　show　that　the　proposed　adaptive　duty　cycle　mechanism　can　effectively　reduce　the　network　delay,　increase　the　network　throughput,　improve　energy　efficiency　of　the　node,　and　effectively　enhance　the　network　performance　in　the　coordination　with　contention　window　adjustment　mechanism.