Embodiments of the present application provide a wireless communication method and device. A network device may send a preamble signal before a downlink signal is sent, so as to assist a terminal device to perform downlink signal detection. The terminal device receives the downlink signal after detecting the preamble signal, thereby avoiding the problem that the complexity and the power consumption are increased because the terminal device needs to perform blind detection on the downlink signal. The method comprises: performing channel detection on a carrier of an unlicensed frequency band; and in the case of the channel detection being successful, sending a preamble signal on the carrier from a first moment, the preamble signal being used for determining that the carrier can be used for transmitting a downlink signal.