Energy efficiency is a primary consideration in a wireless sensor network (WSN).This is also a major parameter when designing a medium access control (MAC) protocol for WSNs.Hierarchical clustering structure is regarded suitable for WSNs due to its good performance in energy conservation.In this work, an adequately flexible mechanism for clustering WSNs is designed, in which some creative or promotional metrics are utilized, such as cluster head selection algorithm, cluster optional reconstruction, interested data transmission, multiple path routing protocol.All these strategies were cooperated to maximize energy saving of whole system.An appropriate MAC protocol for this mechanism is proposed, by flexibly switching the status of diverse sensor nodes in different strategies.The simulation results show that the proposed MAC protocol is suitable for clustering WSNs and performs well in aspects of energy efficiency, flexibility and scalability.