To cope with the problem of energy saving in MANET, we propose a signal-strength-based, graded power control method that operates at MAC layer. By considering the effect of signal fading from realistic environment, and adding processing functions for an array of recently incoming packets at physical layer and MAC layer, nodes can adaptively choose the appropriate transmission power for communication, and enter sleep mode when interference between two ongoing communications occurs. The energy of nodes can be used efficiently, and the network throughput can be enhanced. By emulation in NS-2, we analyze and verify the superiority of our method.