The problem of power and transmission efficiency of Tree-topology large-scale wireless sensor networks（WSNs） is researched and a new MAC protocol based on decomposition and coordination of large-scale network is proposed.The MAC protocol decomposed the network again according to the route information

and a new access algorithm that is adapting it is introduced to the sensor nodes.The experimental results show that the performance of the MAC protocol has lower power consumption and better delivery rate without any addition of delay in evidence.And the protocol can adaptive the large-scale WSNs well.