Based on quantum encryption and Ping-Pong protocol,a quantum secure direct communication protocol was proposed. In this protocol,sender and receiver used n pairs Bell states as carrier,sender entangled single particle in carriers by performing controlled-Not operations and receiver disentangled single particle in carriers also by performing controlled-Not operations. Communication partners performed control mode and message mode in turn. Control mode detects eavesdropping and massage mode sends secret message. Control and message mode did not break Bell states so the process of sharing Bell states was one-time,then communication partners can execute control and message mode again and again to detect eavesdropping and send secret messages.