An improvement of LEACH algorithm was proposed, named LEACH-SMC. The LEACH-SMC protocol algorithm was carried out round by round, and every round was divided into two sections of setup phase and steady station. A critical distance was specified for every cluster head to judge when to use the single-hop or the multi-hop mode between the cluster heads and the base station. The coverage area was greatly improved by the multi-hop manner, and this manner also provided practical value in the nodes distribution in the farm field. It was effective for transmitting the message by single-hop mode, and it could greatly reduce the information delay and packet loss rate too. The coexistence of single-hop and multi-hop can combine the advantages. Simulation results demonstrated that LEACH-SMC protocol could increase network effective coverage area and prolong the network lifetime.