In order to balance the load between cluster head, save the energy consumption of the inter-cluster routing, enhance reliability and flexibility of data transmission, the paper proposes a new clustering routing protocol based on connected graph (CRPCG). The protocol optimizes and innovates in three aspects: cluster head election, clusters formation and clusters routing. Eventually, a connected graph is constituted by the based station and all cluster heads, using the excellent algorithm of the graph theory, to guarantee the network connectivity and reliability, improve the link quality, balance node energy and prolong the network life cycle. The results of simulation show that, the protocol significantly prolong the network life cycle, balance the energy of network nodes, especially in the phase of inter-cluster data transmission, improving the reliability and efficiency of data transmission.